0.6.0

• Breaking change: many parsers that used to explicitly revert changes made to input when parsing fails (a process known as "backtracking") no longer do.

  See our announcement and pull request #108 for more information about the change and its motivation.

  OneOf, which previously did no backtracking whatsoever and trusted other parsers to do the work, is now the main entry point into backtracking behavior.

  Backtracking has been removed from Double.parser(), Parser.filter, Parser.flatMap, Many (with the exception of backtracking a trailing separator), Parser.pipe, PrefixThrough, and PrefixUpTo.

  Note: Peek and Not preserve their backtracking behavior, as they are designed to never consume any input.

• Infrastructure: Add tests for CharacterSet.parse (thanks @andrewjl).