Only digits validator and integer validator for convenience.

I was needing a digits and an integer validator and noticed that I would have to use regexp for this, so I created these two validators. 

I will be contributing with pull requests with things I feel is needed on this library. It's a real tool for me. I thinks this forms library also needs better documentation about using validators, widgets, fields etc. What is best, on the Readme.md or the GitHub Wiki?