rename 3dc to bc5, tweaks to clean stuff up

stb_dxt.h

@@ -30,8 +30,8 @@
 #define STB_DXT_DITHER    1   // use dithering. dubious win. never use for normal maps and the like!
 #define STB_DXT_HIGHQUAL  2   // high quality mode, does two refinement steps instead of 1. ~30-40% slower.
 
-void stb_compress_dxt_block(unsigned char *dest, const unsigned char *src, int alpha, int mode);
-void stb_compress_bc5_block_rg88(unsigned char *dest, const unsigned char *src, int mode);
+void stb_compress_dxt_block(unsigned char *dest, const unsigned char *src_rgba_four_bytes_per_pixel, int alpha, int mode);
+void stb_compress_bc5_block(unsigned char *dest, const unsigned char *src_rg_two_byte_per_pixel, int mode);
 #define STB_COMPRESS_DXT_BLOCK
 
 #ifdef STB_DXT_IMPLEMENTATION
@@ -626,7 +626,7 @@ void stb_compress_dxt_block(unsigned char *dest, const unsigned char *src, int a
    stb__CompressColorBlock(dest,(unsigned char*) src,mode);
 }
 
-void stb_compress_bc5_block_rg88(unsigned char *dest, const unsigned char *src)
+void stb_compress_bc5_block(unsigned char *dest, const unsigned char *src)
 {
    stb__CompressAlphaBlock(dest,(unsigned char*) src,2);
    stb__CompressAlphaBlock(dest + 8,(unsigned char*) src+1,2);