Some functions were missing that in the definition, others weren't,
all had it in the declarations.

Added mention of JPG and HDR formats at the top of the file

jo_jpeg.cpp is a Public Domain JPEG writer written by Jon Olick in 2012
http://www.jonolick.com/code.html

My changes to jo_jpeg:
* port to plain C89 (+ // comments, as supported by MSVC6)
* support for 2 comp input (Greyscale+Alpha, Alpha is ignored)
* use stbi__write_context abstraction instead of stdio for writing
* adjust names to stbiw-style

Conflicts:
	stb_textedit.h