Merge branch 'release/2.2.2' into develop
[DOC] Specify license in gemspec

Fixes #16
[BUGFIX] Ensure that rule refs can be reused when inlining grammars
[FEATURE] Add generator for currency grammar
[DOC] Add documentation on available built-in grammars
[BUGFIX] Currency grammar should match without decimals after a timeout
[FEATURE] Add boolean builtin grammar
[CS] Refactor builtin grammar specs to test interpretation and result in isolation
[BUGFIX] Boolean grammar should interpret as true/false
[CS] Cleanup builtin grammar specs using custom RSpec matchers
[FEATURE] Allow parameterisation of the boolean grammar
[DOC] Match up boolean grammar docs with reality
[CS] Make builtin grammar specs fail nicer with interpretation mismatch
[FEATURE] Add basic grammars for date, digits and number
[FEATURE] Add phone and time builtin grammars
[BUGFIX] Empty input should always be a potential match
[FEATURE] Allow fetching builtin grammars by URI
[CS] Proper error handling when looking up grammars by URI
Merge branch 'feature/builtin_grammars' into develop
[UPDATE] Bump to 2.3.0