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_begin_code.h

@@ -22,11 +22,9 @@
 /* WIKI CATEGORY: BeginCode */
 
 /**
- *  \file SDL_begin_code.h
- *
- *  This file sets things up for C dynamic library function definitions,
- *  static inlined functions, and structures aligned at 4-byte alignment.
- *  If you don't like ugly C preprocessor code, don't look at this file. :)
+ * SDL_begin_code.h sets things up for C dynamic library function definitions,
+ * static inlined functions, and structures aligned at 4-byte alignment.
+ * If you don't like ugly C preprocessor code, don't look at this file. :)
  */
 
 /* This shouldn't be nested -- included it around code only. */