u128 support

[marshallpierce]

Should we move things like the total number of counts to u128? That may have a detrimental affect on performance, especially on lesser hardware; I haven't benchmarked it yet to see.

[jonhoo]

Hmm.. Maybe as a feature? Do we expect u64 to ever not be enough for counts though?

[marshallpierce]

Probably not... u64 is 584 years of 1 billion increments per second. Just figured I'd throw this out to see if anyone had a plausible use case. I'll ask in gitter too.

There are also serialization concerns -- Java already can't represent u64 (only i64) and u128 would be even more hopeless.