clang says:
error: non-constant-expression cannot be narrowed from type 'int'
      to 'unsigned char' in initializer list [-Wc++11-narrowing]

so I explicitly cast affected stuff to unsigned char.

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

tweak license reference wording

stbi_write_hdr_to_func() should still be available even without STBI_WRITE_NO_STDIO,
just like other formats.

Now writing out monochrome bitmaps from 8-bit arrays works
as it does when using PNG.

Bitmaps need 3 bytes per pixel.

Slightly modify the public domain license to keep it in the public domain, but make it clear that even when dedications might not be recognized that the code is still usable.  Given that this isn't dual-licensing under a different license, I'm hoping this will be acceptable.

Slightly modify the public domain license to keep it in the public domain, but make it clear that even when dedications might not be recognized that the code is still usable.  Given that this isn't dual-licensing under a different license, I'm hoping this will be acceptable.

When compiling with more restrictive compiler options
such casting from double to float will cause a warning.

Ex. GCC -Wdouble-promotion
Signed-off-by: NFilip Wasil <filip.wasil@gmail.com>

If calling stbi_write_png concurrently the static array crc_table would be shared between threads causing data-races.

fix internal names to be namspaced properly;

actually want

Add requested flag for controlling TGA RLE compression and fix a
regression when writing monochrome TGAs.

This is the same thing than STB_IMAGE_STATIC of stb_image.h.

When compiling with -O3, gcc would complain that 'linear' might not be
initialized if comp is superior to 4.

In fact passing a value > 4 is an error anyway, but gcc does not know
that.  I changed the switch case to support comp > 4.  I don't think it
should affect the performances.

rename all STBI_ config macros to STBIW_ to avoid conflict with stb_image.h

Fixes #90.