Fix compiler and lint warnings

As discussed in #52, I fixed the compiler and build warnings. 

Most commits are straight-forward. The changes to `PointQuadTree` and `PolyUtil` are covered by unit tests.

Notes:
- As mentioned by you, the usage of the deprecated class `Point` is intentional, so I suppressed the warning
- Handler leaks: the reference to the outer class creates a cyclic reference as long as the instance is alive. However, since instances of these classes are short-lived, it doesn't create a memory leak. For this reason, I disabled the warning instead of refactoring the class.

Please have a look, thanks.