Histogram improvements

[philippjfr]

Cleaned up and made various outstanding fixes for PR #1784.

[philippjfr]

@jlstevens I've now got this passing. Do you still want a label_format parameter as you suggested in the original PR?

[jlstevens]

I still think the label_format idea is a good one, so it would be nice to include if it doesn't add too much additional work.

[philippjfr]

Not sure I like label_format for this, since it's the value dimension label but could be confused with the regular label. Not sure I have much better suggestions though since I don't like vdim_label.

[jlstevens]

So your issue is not with the idea, just the parameter name? How aboutbinned_format or aggregate_label or something like that?

[philippjfr]

frequency_format is probably the most correct. Is that too long?

[jlstevens]

It is a bit long but I think it is ok. I'll try to think of something shorter but if I can't come up with anything, it will do.

[philippjfr]

Actually I probably prefer frequency_label.

[philippjfr]

Tests are now passing (apart from a single transient), so I'll merge. @timothydmorton Thanks again for contributing, sorry this took so long to merge but it'll be in the next release.