Removing tabs in archetype JSON files
Updating data README to use Markdown
Removing EDR file as it's no longer used

Removing the old region format used for holding groups of
maps. EDR files no longer represent map groups since a
directory serves the same purpose nicely.

Also removed the last bit of code commenting mentioning EDR.
Updating data README file
Removing glFlush from GraphicsUtil::flipScreen

SDL_GL_SwapWindow causes buffers to be swapped and thus it is
already causing a glFlush to occur behind the scenes. In other words, SDL_GL_SwapWindow *renders* glFlush redundant. Heh heh.