Refactor validator helper

1. Passes the request and reply objects to the callbacks to allow for handling without having to spawn per-request closure instances.
2. Remove the RegExp construction in favor of passing the literal in via the options hash. This is more performant and helps the users avoid surprises when presumed literals are parsed as regular expressions.
Update API docs
Merge pull request #6 from walmartlabs/validator-refactor

Refactor validator helper