The handler's now go to their relative paths like they should.

Before they went to the relative path sometimes when it was the default
handler (I think it was that way anyway), but other than that they still
had their key in the path. That is not the case anymore.
Variable checking exists.

If you pass in an `Integer` in a path that requests a `Float`, the
`howCorrect` method will return `0`.

Also added another handler called the addHandler which adds things.
MERGED?
Merge branch 'path-tests-dk' of github.com:dkuntz2/java-httpserver into path-tests-dk