Neutralize case for server side messages

It can be helpful if messages use upper case on server side (e.g. Java enums).
Add custom notify method

Custom notify method can be useful if message severity is known as string at the
callpoint. It helps to avoid code like `growl[severity](text, config)` which is
tricky and error-prone.
Merge pull request #41 from madhead/master

Adding general growl method for sending growls when the severity is a text variable.