Version 0.3
* Added `->requires`, `->excludes`, and `->envname` from [Plumbum](http://plumbum. readthedocs.io/en/latest/)
* Supports `->mandatory` from Plubmum
* More tests for help strings, improvements in formatting
* Support type and set syntax in positionals help strings
* Added help groups, with `->group("name")` syntax
* Added initial support for ini file reading with `add_config` option.
* Supports GCC 4.7 again
* Clang 3.5 now required for tests due to googlemock usage, 3.4 should still work otherwise
* Changes `setup` for an explicit help bool in constructor/`add_subcommand`