Fix for Java 13 compatibility #23

[markbastian]

Fix entailed added type hints to resolve breaking code. All unit tests pass. No reflection errors in core ns. I did not update project dependencies to minimize project changes but this might be a good idea as well.

[slipset]

@markbastian would you be interested in following up on this work now? I can release a new version once this is approved, perhaps by @ztellman ?

[markbastian]

Absolutely! I haven't looked at this in ages but it should still be good to go.

[boxxxie]

i tested these changes, i'm not sure what the process is for merging, but for the few people who use this lib, i think merging and making a release would be welcome.