Add CODING_STYLE document to standardize on some style issues.

Standardize brace handling around all else clauses according to new CODING_STYLE guidelines.

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+Cairo coding style.
+
+This document is intended to be a short description of the preferred
+coding style for the cairo source code. Good style requires good
+taste, which means this can't all be reduced to automated rules, and
+there are exceptions.
+
+We want the code to be easy to understand and maintain, and consistent
+style plays an important part in that, even if some of the specific
+details seem trivial. If nothing else, this document gives a place to
+put consistent answers for issues that would otherwise be arbitrary.
+
+Most of the guidelines here are demonstrated by examples, (which means
+this document is quicker to read than it might appear given its
+length). Most of the examples are positive examples that you should
+imitate. The few negative examples are clearly marked with a comment
+of /* Yuck! */. Please don't submit code to cairo that looks like any
+of these.
+
+Indentation
+-----------
+Each new level is indented 4 more spaces than the previous level:
+
+	if (condition)
+	    do_something ();
+
+Spaces or tabs (or a combination) can be used in indentation, but tabs
+must always be interpreted as 8 spaces. Code using single tabs for all
+indentation (expecting people to interpret tabs as 4 spaces) will not
+be accepted in cairo.
+
+The rationale here is that tabs are used in the code for lining things
+up other than indentation, (see the Whitespace section below), and
+changing the interpretation of tab from 8 characters will break this.
+
+Braces
+------
+Most of the code in cairo uses bracing in the style of K&R:
+
+	if (condition) {
+	    do_this ();
+	    do_that ();
+	} else {
+	    do_the_other ();
+	}
+
+but some of the code uses an alternate style:
+
+	if (condition)
+	{
+	    do_this ();
+	    do_that ();
+	}
+	else
+	{
+	    do_the_other ();
+	}
+
+and that seems just fine. We won't lay down any strict rule on this
+point, (though there should be some local). If you came here hoping to
+find some guidance, then use the first form above.
+
+If all of the substatements of an if statement are single statements,
+the optional braces should not usually appear:
+
+	if (condition)
+	    do_this ();
+	else
+	    do_that ();
+
+But the braces are mandatory when mixing single statement and compund
+statements in the various clauses. For example, do not do this:
+
+	if (condition) {
+	    do_this ();
+	    do_that ();
+	} else			/* Yuck! */
+	    do_the_other ();
+
+And of course, there are exceptions for when the code just looks
+better with the braces:
+
+	if (condition) {
+	    /* Note that we have to be careful here. */
+	    do_something_dangerous (with_care);
+	}
+
+	if (condition &&
+	    other_condition &&
+	    yet_another)
+	{
+	    do_something ();
+	}
+
+And note that this last example also shows a situtation in which the
+opening brace really needs to be on its own line. The following looks awful:
+
+	if (condition &&
+	    other_condition &&
+	    yet_another) {	/* Yuck! */
+	    do_something ();
+	}
+
+As we said above, legible code that is easy to understand and maintain
+is the goal, not adherence to strict rules.
+
+Whitespace
+----------
+Separate logically distinct chunks with a single newline. This
+obviously applies between functions, but also applies within a
+function or block and can even be used to good effect within a
+structure definition:
+
+	struct _cairo_gstate {
+	    cairo_operator_t operator;
+    
+	    double tolerance;
+
+	    /* stroke style */
+	    double line_width;
+	    cairo_line_cap_t line_cap;
+	    cairo_line_join_t line_join;
+	    double miter_limit;
+
+	    cairo_fill_rule_t fill_rule;
+
+	    double *dash;
+	    int num_dashes;
+	    double dash_offset;
+	
+	    ...
+	}
+
+Use a single space before a left parenthesis, except where the
+standard will not allow it, (eg. when defining a parameterized macro).
+
+Don't eliminate whitespace just because things would still fit on one
+line. This breaks the expected visual structure of the code making it
+much harder to read and understand:
+
+	if (condition) foo (); else bar ();	/* Yuck! */
+
+As a special case of the bracing and whitespace guidelines, function
+definitions should always take the following form:
+
+	void
+	my_function (argument)
+	{
+	    do_my_things ();
+	}
+
+And function prototypes should similarly have the return type (and
+associated specifiers and qualifiers) on a line above the function, so
+that the function name is flush left.
+
+Break up long line (> ~80 characters) and use whitespace to align
+things nicely. For example the arguments in a long list to a function call should all be aligned with each other:
+
+	align_function_arguments (argument_the_first,
+				  argument_the_second,
+				  argument_the_third);
+
+And as a special rule, in a function prototype, (as well as in the
+definition), whitespace should be inserted between the parameter types
+and names so that the names are aligned:
+
+	void
+	align_parameter_names_in_prototypes (const char *char_star_arg,
+					     int	 int_arg,
+					     double	*double_star_arg,
+					     double	 duble_arg);
+
+Note that parameters with a * prefix are aligned one character to the
+left so that the actual names are aligned.
+
+Managing nested blocks
+----------------------
+Long blocks that are deeply nested make the code very hard to
+read. Fortunately such blocks often indicate logically distinct chunks
+of functionality that are begging to be split into their own
+functions. Please listen to the blocks when they beg.
+
+In other cases, gratuitous nesting comes about because the primary
+functionality gets buried in a nested block rather than living at the
+primary level where it belongs. Consider the following:
+
+	foo = malloc (sizeof (foo_t));
+	if (foo) {					/* Yuck! */
+	    ...
+	    /* lots of code to initialize foo */
+	    ...
+	    return SUCCESS;
+	}
+	return FAILURE;
+
+This kind of gratuitous nesting can be avoided by following a pattern
+of handling exceptional cases early and returning:
+
+	foo = malloc (sizeof (foo_t));
+	if (foo == NULL)
+	    return FAILURE;
+
+	...
+	/* lots of code to initialize foo */
+	...
+	return SUCCESS;
+
+The return statement is often the best thing to use in a pattern like
+this. If it's not available due to additional nesting above which
+require some cleanup after the current block, then consider splitting
+the current block into a new function before using goto.