Fully naming abbreviation-named units

[JohelEGP]

A few units, like dB and ppm, are named after their abbreviation, rather than their full name, like decibels and parts_per_million, respectively. I think these should be expanded as shown.

[nholthaus]

By design. I originally had those units that way, but the abbreviations are so much more canonical than the actual names that it was confusing.

[nholthaus]

another weird one is the unit henry. It has two plural forms, equally used, henrys and henries. I just picked one.

[JohelEGP]

Won't these get in the way of #196?

[nholthaus]

hrm, yes. I'll expand them.

[nholthaus]

I think this was solved with #256, sans non-linear scales, which we're intentionally leaving out.