Package has no tests

[mauritsvanrees]

plone.schema has plone.app.testing in its extras_require in setup.py, but it does not actually have tests. We should create some.

I was wondering if the email regular expression needed improvement. For example test@example.museum seemed like it would not be matched as valid, but in fact it is matched, so there is no problem.
But if someone would want to improve it, tests would be helpful there.

[gyst]

Fixed in #40