resolves #1110 enable TeX equation auto-numbering if eqnums is set

* set autoNumber to eqnums attribute value if defined
  - if defined, possible values are none, all, AMS or empty (empty becomes AMS)
* set autoNumber to AMS if eqnums attribute value is empty
* autoNumber is set to "none" if eqnums attribute is not defined
Merge pull request #1202 from mojavelinux/issue-1110

resolves #1110 enable TeX equation auto-numbering if eqnums is set