docs: heavy editing to make this happy with latest wikibridge.

The public headers saw lots of cleanups, backporting from SDL3 docs, and
merging with the wiki.

The markdown files in docs/README-*.md were converted to Unix endlines.

include/SDL_quit.h

@@ -34,7 +34,7 @@
 /**
  *  \file SDL_quit.h
  *
- *  An ::SDL_QUIT event is generated when the user tries to close the application
+ *  An SDL_QUIT event is generated when the user tries to close the application
  *  window.  If it is ignored or filtered out, the window will remain open.
  *  If it is not ignored or filtered, it is queued normally and the window
  *  is allowed to close.  When the window is closed, screen updates will
@@ -42,8 +42,8 @@
  *
  *  SDL_Init() installs signal handlers for SIGINT (keyboard interrupt)
  *  and SIGTERM (system termination request), if handlers do not already
- *  exist, that generate ::SDL_QUIT events as well.  There is no way
- *  to determine the cause of an ::SDL_QUIT event, but setting a signal
+ *  exist, that generate SDL_QUIT events as well.  There is no way
+ *  to determine the cause of an SDL_QUIT event, but setting a signal
  *  handler in your application will override the default generation of
  *  quit events for that signal.
  *