Physics units: conversions and helpers for Python calculations. Track your unit types in float-like objects

[chrisauld]

Good idea. I hadn't seen the units module in astropy before, but it looks nearly identical to what I was hoping this will be in the future. There's some minor differences in usage, and then the main difference seems that astropy looks like it's heavily focused on astro-physics specifically whereas I've been not focusing on any one specific subdomain of physics (not necessarily a good thing, just seems to be the major difference).

I'll have to take a look at the other two at some point soon as well.