Port to older compilers, the newer ones accept C-style constructs! wtf

Readme changes

update readme

fix deprecation

Fix saving of negative pitch GIF.

Fix assertion in adhoc layout detection.

Negative trailing pixels would be found, which could cause a useless realloc.

Fix Issue #63

Optimizing, removing old decoder.

Reinstante Miniz decoding for PNG.

Add test to avoid this #54 regression. Miniz decoding reverted until …

…a fix is found.