added inside callback for geofences

[codearachnid]

I wanted to be able to track movements between the fence not just if position crossed ouside threshhold. So by adding an option for an inside callback it can now track in either direction and callback if marker stays within or ouside boundary on movement.

[codearachnid]

I apologize for the 3 commits - was using the github web api to make these edits since I don't have access to run the git repo locally and commit.

[xenda]

This looks interesting. Would you mind adding a test for it?

[codearachnid]

I can work on including a test for it. I didn't see any existing geofence tests and this just extends the current implementation to subscribe to movements in/out.

[ncacace]

Suggestion:
Instead of 'Outside' and 'Inside'
Why not true/false switch for current outside option since you're either inside or outside and then add it as a parameter..?

This would be useful if you're waiting for someone to arrive and wanted to be notified if they arrived within a certain range of a perimeter for example