Added some JavaDoc.
Moved the Tools up a level in the package tree because I'm sick of digging in to get them.
Made fields private.
Added tests for Connection class.
Removed unused import.
Added JavaDoc.
Added tests for ConnectionType.
Added tests for Exit class.
Added tests for ExitBuilder.  Note that complete branch coverage has not been achieved.  My reasoning is that for the last remaining branch, i.e. the passing in of a Cell with a potential exit type of X, the methods called by that branch has already been exercised.  Without exposing those methods (to Mockito, for example) it's not possible to test them.  It might be with PowerMock, but it's probably pointless here.  Rather it's probably better to stick with the principle that you shouldn't need to test private methods.