Added initial command line implementation
Refactored rt executable:

* Don't use subcommands. It makes help very confusing. Also it's not necessary. rt is our primary command, and the compare/convert/export/... thor commands appear like subcommands on the command line.
* Add Rtfile loading and DSL
* Move generic parts of rt into kramdown-repositext
* change rt namespace to be consistent with current conventions
Extracted long_descriptions into module so that we can override them in vgr-repositext
Ignore existing rtfile on rt init command
Replace example Rtfile DSL methods with first real one
Added config to Rt
Added Outcome.rb as a dependency
Renamed rt executable to repositext
Updated Rt::Config, added parsers
Renamed Repositext::Rt to Repositext::Cli to make more obvious what it is.
Updated rubyzip gem to address bug when initializing Zip::File from string. Update Parser::Idml interface to accept file contents instead of file name.
Fixed name error
Refactored Cli::Config and Dsl
Moved CLI commands into separate folder
Added FakeFS for testing
Refactored API for Repositext::Cli::Config initialize (don't need Cli instance)
Changed API for Repositext::Cli::Config#add_file_pattern: Allow both string and block form.
Improved Repositext::Cli::Utils
Updated specs and documentation
Replaced all instances of STDERR with $stderr so that we can redirect/capture output during testing.