Add max_length to Email (254) & update .gitignore

According to links
http://stackoverflow.com/questions/386294/what-is-the-maximum-length-of-a-valid-email-address
http://www.rfc-editor.org/errata_search.php?rfc=3696&eid=1690
limit is 254.
In current version I can do:
```
t.Email().check('x' * 100000 + '@ukr.net')
```
and it's valid.
I don't see why we need these strings at all. String class will set up max and min length anyway, so this is just redundant.