Added RE2 RegexOption that changes parser behavior to include more RE…

…2 formats that the .NET engine does not support. This will allow a smoother transition from the stdlib regexp package.

fix error added during scanning of numeric backreferences with groups

fix issue with groups containing slash constructs like (\c[)

add fuzzing tests for syntax package, fix issues discovered by fuzzing

Add benchmark to match go stdlib

add more detail about code history to ATTRIB file. fixes dlclark#11

prevent panic with multi-byte unicode bmPrefix that partially match. f…

…ixes dlclark#6

prevent panic when using 2-byte unicode bmPrefix against 3-byte input…

… values. fixes dlclark#5

fix ECMAScript mode -- merge branch 'dop251-ecmascript'

add ReplaceFunc to support MatchEvaluator custom replacement functions. 

fixes dlclark#3