User creation

Add the ability to create users. Tests and validations also created as necessary.
Note on this: I've heard that many email regexes tend to be fairly restrictive, so I used one that I'd written for a networking class (making some minor edits to port it from Java to Ruby). It was based on the format of an email that I believe came from the IETF (the professor gave us what he said was an official format of some sort, and I wrote the regex to follow it). Any thoughts on whether I should keep using this or just switch to some other (either now or as a standard in the future) would be appreciated.