Please add upright greeks

[tonyriverms]

The upright greeks like $\rm{\alpha}$ does not work, and $\bf{\rm\{\alpha}}$ does not work either. I searched online and it looks mathjax current does not support that. I believe these notations are not uncommonly used. Adding support for them could be very helpful for those in the field of numerical computation who frequently use these upright greeks to represent coefficient vectors.

[dpvc]

This is a duplicate of #1076. See also #1859.

[dpvc]

The upgreek package now allows access to upright Greek letters. It is new in v3.2.