Objective-C: Implement CLI

[aslakhellesoy]

This issue is for remaining work of #240 related to Objective-C:

• [ ] Print errors as ndjson
• [ ] Replace bin/gherkin-generate-ast with a new bin/gherkin
• [ ] Implement stream API
• [ ] Implement a pickles compiler and use it in stream API and bin/gherkin

@LiohAu / @joshski / @Ahmed-Ali - any takers?

[aslakhellesoy]

This issue was moved to cucumber/cucumber#146