Initial changes and test for multi-line filtering

Reference #54, I've created some initial changes to allow multi-line regex to function. 

This makes use of a defined sized line buffer that regexs can be run against. With line buffer size set to 1, should function as if line buffer doesn't even exist, therefore maintaining compatibility with current configurations.

I don't have any great examples of multi-line logs in order to test fully. Does anyone have a log file they could contribute, maybe with example failregex?

Having thought about it, maybe the maxlines option should be in specific filter.conf?