Comment typo
Provide tasty option to load assets externally

This is still very coarse but should do the job, if you don't want to
inline assets.

Some changes were *stolen* from larsrh@5db2d6b9f2fa6373114c8b672cb273361c5f982e

See #14.
No need for script type attribute in HTML5
Catch exceptions when formatting test messages

Fixes https://github.com/feuerbach/tasty-html/issues/15