* Callback for `from`
Added a callback for `from`, which takes file as an argument. Allows the user to tailor the search string according to the filename.
* Minor Changes to Callback for `from`
Additional comments to explain the callback forms.
Reversed minor version bump.
* Changes to documentation for `to` callback
Reverted to original `to` callback example.
Added a separate example example for using the `file` argument.
* Pass filename as last arg to replacer function
* - Cleaned up replacer function override to use ES6
- Added replacer function tests to Async callback & Sync specs
