(maint) Fix where cfacter get installed to.

Now that we don't build cfacter's dependencies, change back to installing cfacter to /usr/local/[bin|lib] by default.
(CFACT-20) Implement JSON output.

Implementing JSON output of facts.
Implementing map_value to support complex fact values.
Implementing integer_value to support integer types in JSON output.
Fixing output of existing integer types.
Normalizing fact names taken on the command line.
(maint) Add more unit tests.

Adding tests for:

- facter::util::file
- facter::util::option_set
- facter::execution::posix
(maint) Add test target to cmake output.

Adding a test target to cmake output so tests can be run with just "make test".
Updating travis to run tests through ctest.
Updating README to cover running tests.