dev branch: force uint64 bitmaps
prep work for creating variable-sized tables
three versions of perf tests running OK
w, t, etc, now Table attributes
tests parameterized, w = 4,5,6
added w=4,5,6,7,8 HAMT perf tests
Merge branch 'master' into dev

Conflicts:
	TODO
	hamt64_perf_test.go
	table32.go
	table64.go