Extend and improve tests, small fixes
Restructure OpTreeContext, replace `nTimes` with improved `X.times(...)`
Add support for `.separatedBy`, more refactorings
Add NOTHING rule
Improve internal naming
Simplify Rule model and EMPTY and NOTHING rules
Add `anyOf` rule primitive
Add CharPredicate and CharUtils
Upgrade to specs2 2.3.6
Add first-class support for CharPredicates as Rule0
Add `ignoreCase` rule primitive