[change] Trim zeros after round and make pad independent

[Mc-Zen]

Trailing zeros are now stripped after rounding. Padding is then applied, even if the number was rounded (in order to maybe recover zeros).

This results in one effective change:

Before: num(round: (precision: 2, pad: false)[0.299] -> $0.30$

Now: num(round: (precision: 2, pad: false)[0.299] -> $0.3$

Fixes the issue

At first it now feels to me like the rounding step should do 0.2999 -> 0.3 instead of 0.2999 -> 0.300 so that the result 0.300 should only happen through padding afterwards.

from #66 (comment).