Did the tag thing (issue #4)

I think I did it right, although maybe I'm supposed to call tag.delete() instead of session.delete(tag)...
Added basic email/password restrictions

I'd like to expand the current validation system a little (so that you can define several validation tests for each field nicely and you can report to the user all errors at once instead of only one per validation attempt) but that goes in another commit.
Changed sidebar color
Changed sidebar color (again, sorry, I changed my mind)
Merge pull request #8 from slapresta/patch-1

Did the tag thing (fixes #4)
Merge pull request #9 from slapresta/patch-2

Added basic email/password restrictions
Added multiple validation errors
Nicely formatted error messages
Merge branch 'validation-errors' of http://github.com/slapresta/hat into validation-errors