object for some common regexs

[johnynek]

It would be cool to have an object with some common regexs:

1. integers: signed, nonneg, positive, int32, int64, also floating point etc...
2. base-encoded binary: 8, 16, 32, 64, etc... (also some esoteric ones)
3. there are super complex regexs for email, urls, etc... would be nice to have those.

With these, you can do some neat tricks showing that some things are subsets of others, or that there is no valid email that is also a url, or something...