(CFACT-66) Remove log4cxx

Replaced log4cxx with Boost.Log. Supports a similar structure of configuring formatted
sinks for output, with filtering based on log_level.
(CFACT-66) Update trace and readme, add comments, and re-org.

Added macros for log_level::trace.
Updated README to reflect removing log4cxx.
Added comments for new functions in logging.
Change logging prefix used for execution output to differentiate it.
Re-organized logging source so only colorizing is OS-specific.
Merge pull request #85 from MikaelSmith/task/master/CFACT-66-replace-log4cxx

(CFACT-66) Remove log4cxx