Convert JBOOLEAN_USE_MOZ_DEFAULTS into an integer "compression profile" parameter
This eliminates JBOOLEAN_USE_MOZ_DEFAULTS and replaces it with
JINT_COMPRESS_PROFILE, a more flexible and descriptive parameter.  Currently,
this new parameter works in much the same way as the old-- it changes the
behavior of jpeg_set_defaults().  It currently supports only two values
(max. compression, i.e. mozjpeg defaults, and fastest, i.e. libjpeg-turbo
defaults), but it can be extended in the future with additional profiles that
balance compression ratio with performance.
Rename jccompat.c to jcext.c
"jcext" is a bit more descriptive, since this code is primarily intended to
extend the libjpeg API.  It does so in a backward-ABI-compatible manner, but
"jccompat" could be misinterpreted to mean that the code is providing backward
compatibility at the code level..
Merge pull request #133 from dcommander/jpeg_set_compress_profile

Change JBOOLEAN_USE_MOZ_DEFAULTS to an integer parameter