(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
(maint) Disable warning register-deprecated.

This warning is specific to Clang, and marks register as deprecated.
Boost still uses register, and we're unlikely to (plus it doesn't
cause any harm when it's used), so the warning is now disabled.
Merge pull request #87 from MikaelSmith/maint/master/Disable-register-deprecated-warning

(maint) Disable warning register-deprecated.
(CFACT-44) Add missing Facter.version method.

Adding a missing Facter.version method that returns
Facter::FACTERVERSION.
(CFACT-44) Support boolean values in confines.

Support true and false in a Ruby confine hash.
(CFACT-44) Implement exec and which on Facter::Util::Resolution.

Implementing exec and which singleton methods on
Facter::Util::Resolution.

These call directly into the corresponding methods on Facter::Core::Execution.
(foo)
(bar)