Review: Support for per-shot looks

Jeremy Selan <jeremy...@...>


Resolves Issue #16:

This commit enables color transforms to leverage environment variables
+ search paths to determine the lut location. This will enable
workflows where the looks changes across different
shots/sequences/etc. For apps which work in the context of a single
shot, no changes are required. And, for apps which span multiple
shots (such as a playback utility), a mechanism is provided to update
the variables at runtime.

We introduce a new class, OCIO::Context, that is responsible for all
of the work involved in turning a short filename into full path. (it
handles both envvar interpolation and search paths). Profiles, on
construction, automatically get a default context which contains the
full environment. New versions of getProcessor have been added that
take a context as an argument, allowing the default context to be
overridden at runtime. If no context is provided, the default is

-- Jeremy

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