tests: Rename functional -> func

Each time I try to run a single functional test, such as...

    $ crucible run functional.blah.sub-blah

...I dread typing out "functional". It's too verbose. The shorter "func"
is a fine replacement.

Move directory src/functional -> src/func and update all docs.

1 files changed, 1 insertions, 1 deletions

diff --git a/HACKING b/HACKING
index c63e5ce..3994385 100644
--- a/HACKING
+++ b/HACKING
@@ -26,7 +26,7 @@ Directory Layout
   Example tests that demonstrate how to use the framework or how to accomplish
   a tricky testing task.
 
-- src/tests/functional
+- src/tests/func
   Functional tests, such as
       - Draw a triangle, then verify the render target contains a triangle.
       - Load an image file, generate a mipmap, then compare it against it