fix incorrect initialization of alpha channel for RGB PSD

- conversion from int to stbi_uc
- unused parameter

fix bug where we couldn't rewind a file that reached EOF, which can happen with < 92-byte PIC,PNM,HDR,TGA

adjust credits

fix bug in reedbeta patch

The warning concerns the return value of stbi_err, which is an int, being converted to a pointer. In VS2015 it seems casting directly from a 32-bit int to a 64-bit pointer triggers this warning. Worked around by first converting to a 64-bit int (here size_t) and then to a pointer.

- Fixed possible memory leak.
- Fix for transparent backgrounds.
- Adapted internal function to allow proper animation loading.

actually want

Incorrect endianness hilariously doesn't manifest _if_ the original
image was upconverted from 8-bit to 16-bit.

0xffff would accidentally round to 0x10000.

This extends the current PSD loader to add support for 16-bit images, by
quantizing them down to 8-bit upon load.

It was incorrectly setting the wrong field to NULL, causing it to get
freed again later.

stb_voxel_render.h: fix STBVOX_CONFIG_OPTIMIZED_VHEIGHT

The original AC decoding logic handled ZRL (runs of 16 zeros)
incorrectly.

The problem is that the original flow set r=16 and skipped the
final coeff write when s=0. This is not actually correct. The
problem is the intervening "refinement" bits.

With the original logic, even once we decrement r to 0, we keep
reading more refinement bits for subsequent coefficients until
we find the next currently-unsent AC in the current scan. That is,
it works as if it was trying to place 17 new AC values, and only
bails at the last minute from actually setting that 17th value.

This is wrong. Once we've found the 16th previously-unsent AC, we
need to stop reading refinement bits, otherwise we get out of sync
with the bit stream (which expects us to read a huffman code next).

The easiest fix is to just do what the JPEG standard implicitly
assumes anyway: treat ZRL as a run of 15 zeros followed by an
explicit magnitude-zero AC coeff. (That is, leave s=0 and actually
write s). So this is what this fix does.

 more consistent name,
 refactor stbi_load_main to preserve old code,
 support float HDR path,
 minor bugfix

bump version and update credits;
minor whitespace changes;

GCC 4.7 gave the warning "signed and unsigned type in conditional
expression" because the ternary operator mixes signed and unsigned
integers. Fixed by casting to unsigned inside the "if" branch instead
of casting the result of the entire conditional.

This fixes two things. First, the logic to disable SSE2 on
GCC unless "-msse2" was not specific enough, and ended up
disabling SIMD support on NEON targets entirely. Shuffle
the detection logic around to make that bit x86-specific.

Second, 32-bit MinGW assumes 16-byte aligned stacks, but this is
not in the Windows ABI and hence DLLs and callbacks don't
necessarily provide it. This caused a crash.

This can be fixed by providing the right command-line option,
which we have no control over. As a compromise, disable the SSE2
path on MinGW unless a specific #define explained in the comments
is set. That way, we default to safe (never-crashing) behavior
unless the user explicitly signals they know what they're doing.

fix incorrectly-named assert, attempt to fix (char) cast warning (tricky since char's signedness is unknown)