Added Solar units of measure

[robotsnowfall]

Measure	Unit	Reference
Length	(Nominal) Solar Radius	https://en.wikipedia.org/wiki/Solar_radius
Power	Solar Luminosity	https://en.wikipedia.org/wiki/Solar_luminosity
Mass	Solar Mass	https://en.wikipedia.org/wiki/Solar_mass

First time submission, let me know if I missed something.

[derekmorr]

Thanks for the patch. The changes look good (I had to double check that some of the changes didn't belong in the radio package, but I think they're good where they are).

A few questions:

• Should nominal solar radius be added as well?
• Are there alternate symbols that don't involve unicode symbols? In the past, some users have raised objections about certain symbols being difficult to enter on a keyboard.

[robotsnowfall]

I think having nominal solar radius would be useful, yes. I have a patch that adds it.

As for the unicode symbols, I totally see where you're coming from. I saw the symbol for Angstrom (Å) was already in the repo, so I didn't think it would be too much of a stretch. There doesn't seem to be generally accepted symbols other than the ones provided. I suppose we could make them up though? There would be a danger of overlap if we chose something like SR or RS for solar radius, or SL/LS for solar luminosity, etc.

[cquiroz]

Thanks, it looks good to me.
I'm ok with unicode units if they are in common use or officially accepted for the unit

[derekmorr]

Ok, the patch looks good to me.

I'd rather not invent new symbols. If there are only unicode symbols, then we'll use them.

Thanks again for the PR!