newRPL: Angles revisited

[Claudio L.]

Since I can't find a way to make things work correctly, I think we should drop the part that doesn't work and simplify:

* Tagged angles could be used for user entry.
* Tagged angles could be used for return values of trig functions.
* Any operation (I mean any) done on a tagged angle will convert it to the current angle system and remove the tag prior to doing the operation itself.
* Commands will exist to convert between all tag formats, and to explicitly tag a number.

I know it will eliminate many of the useful features (like directly adding/subtracting angles in DMS), but at least won't introduce any weirdness.