wikiheaders: bridge wiki Category docs to the headers!

Did an initial cleanup on the headers and wrote a few pieces of documentation,
but this needs more work to fill out the documentation.

include/SDL3/SDL_test_assert.h

@@ -20,8 +20,6 @@
 */
 
 /**
- *  \file SDL_test_assert.h
- *
  *  Assertion functions of SDL test framework.
  *
  *  This code is a part of the SDL test library, not the main SDL library.