Fixes offset overflow in retile
Apply OCIO looks

Exposed on the command line as oiiotool --ociolook.
From C++, you still use IBA::colorconvert, but using a ColorProcessor that
you get with new call: ColorConfig::createLookTransform().
Use find_tile in get_tile so that tile microcache is properly updated
Document ImageBuf in the programming guide

Some extremely minor changes to imagebuf.h as well -- change some parameter
names, rewrite comments, reorder a couple declarations.  No functional or
compatibility changes at all... just making things clearer for the reader,
stuff I noticed could be improved while writing the docs.
Rebuild PDF docs
Simplify oiiotool --text argument parsing by using modern style
CHANGES update
Remove unused references to shared_mutex
For deep files, fix some subtle problems with differing per-channel formats
Turn off openssl-related warnings on OSX.
On newer OSX releases, Apple has marked the functions in openssl/sha.h
as deprecated.
JPEG - found a magic number variant we didn't recognize