Version of compare-bytes that does unsigned comparisons.

Could use some more work to speed it up; I've had a heck of a time
getting clojure to do primitive math on byte objects, and it's very
wasteful to: box to Byte; check it's a Number; convert to Long;
unbox to long; do math; downgrade to byte; upgrade *back* to a long;
compare with (long)0.
Do some more primitive math
Fix signedness
Add test for compare-bytes
rearrange compare-bytes a bit
Merge branch 'unsigned-compare-bytes' into develop
0.10.4, fixing compare-bytes
Make (map-keys nil f) return nil.

Similarly for filter-keys, and that whole family of functions.
This is so that (update {} :k map-keys f) doesn't return {:k {}}.
0.10.5
0.10.6 - at long last, `ap`!