Adds support for rules_swift 2.x.

[luispadron]

This does force users using this version of sourcekitten to also use rules_swift because of the swift_c_module removal.

Outstanding issues:

• [x] max_compatibility_level needs to be updated for deps that use rules_swift
• [x] Need a real 2.0.0 release before we can move of the release candidate

Requires the following:

• https://github.com/jpsim/Yams/pull/420