Implement a LaTeX command to draw over arc

Created by: fred-wang

We don't seem to have any command to draw an over arc. See

https://groups.google.com/forum/#!searchin/mathjax-users/arc/mathjax-users/1cmdK1pJqeg/iEI4yMgcZdQJ https://groups.google.com/forum/#!searchin/mathjax-users/arc/mathjax-users/OQ5abHvfHOI/sIYs73G5HKAJ https://groups.google.com/forum/#!searchin/mathjax-users/arc/mathjax-users/x0nbdr9c47o/mwcTCudgV-MJ

and on Wikipedia: https://bugzilla.wikimedia.org/show_bug.cgi?id=30215

Possible candidates seem to be \overarc, \widearc or \wideparent: http://tex.stackexchange.com/questions/15468/frown-and-mathop-stackrel-overset