(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.
(maint) Remove incorrect doc comment in #ifdef'd code.

Removing extraneous template argument doc comment.
Merge pull request #86 from peterhuene/custom/facts

(CFACT-44) More fixes for Ruby compatibility.
(CFACT-44) Bind to loaded Ruby (if present) instead of searching.

Currently we always search the file system for a Ruby library.
While we do check to see if the library found has already loaded,
if libfacter finds a different library than the already loaded Ruby
library, a separate VM will be created that will be isolated from
the original VM.  This would prevent facts from populating correctly.

POSIX libdl (and Windows through a different mechanism) has a way
for us to bind to the loaded Ruby without having to search the file
system.  Specifically, dlsym will search for symbols exported by
the initially loaded objects and any objects that were loaded as
global.  Ruby thankfully links against libruby such that we can
discover libruby's exports this way.  When libfacter is running
under Ruby, we should now reliably function under the same Ruby VM.
(CFACT-44) Allow Ruby classes to be instantiated from Ruby.

Currently the Ruby classes implemented in libfacter can only be
instantiated from C++. If one of the classes is instantiated from Ruby,
we fail to associate the Ruby instance with the underlying C++ type.

To fix this, define an allocation, mark, and free callback for each type
we support allocating from Ruby.  The allocate function is responsible
for creating the underlying C++ type when the Ruby type is allocated.
The mark function is responsible for marking referenced VALUEs during
the mark phase of GC.  The free function is responsible for freeing the
underlying C++ type when the GC deallocates the Ruby object.
(CFACT-44) Replace cfacter gem with libfacter Ruby API.

The cfacter gem implementation is unnecessary now that we implement the
Ruby API in libfacter.  Therefore, remove it in favor of directly
calling into libfacter from Ruby.

To implement the gem's behavior, the C++ Facter module implementation
now implements the following methods:

* Facter.flush (and implemented on_flush in resolutions)
* Facter.list
* Facter.to_hash
* Facter.each
* Facter.clear
* Facter.reset
* Facter.loadfacts
* Facter.search
* Facter.search_path
* Facter.search_external
* Facter.search_external_path

Additionally, the logic for loading Ruby facts has moved out of the
collection (where it didn't belong) and moved into the C++ Facter
module.

We now follow the old Facter's loading design of first trying
to load a fact by file name and then falling back to loading all facts
if the fact can't be found.