copy class attribute from base document when splitting
I think when restoring text mode, need to allow for display math as well
fix ams's \tag command
cleanup RefStepCounter; make DefMath with TeX code for presentation work correctly
fix order of arguments to tabularx (Thanks giovanni111)
added a 'notes' entry to suggest installing a TeX
Proper support for left aligned equations (fleqn)
proper support for left,right, centered equations