No embedded docs for (some?) units

[gwhitney]

With the restored autocomplete facility in the demo, I discovered that mathjs knows about the units 'candela' and 'angstrom'. As these seem somewhat esoteric, I tried help(candela) and help('candela') (and similarly for angstrom) in the homepage demo, and all of these calls returned Error: No documentation found on "candela".

There should be (1) a test that all appropriate symbols have embedded docs, and (2) all units should have embedded docs.

[josdejong]

I think help doesn't work for any unit. Would be nice to extend help to support units too!