Convert and Drop Units

[tjwixtrom]

In working on #468 and #454 as well as others, it has become apparent that there is a need for a function that will convert inputs to common units and then remove units, returning just the magnitudes. Based on comments from @dopplershift in #468 , this is a stab at solving that problem with the hope that it can shorten some existing code doing the same operations in other functions.

[tjwixtrom]

Looks like a @units.wrap decorator can be used in place of this to handle unit conversion and dropping (see latest commit of #468). This can be saved if the unit wrap doesn't work in other function that need to convert and drop units and otherwise scrapped in place of @units.wrap.

[dopplershift]

I'll close this for now but we can re-open if we decide we need to replace @wraps