Remove dependencies of TeX->MathML conversion on the choice of fonts (TeX versus STIX). This no longer worked since the input and output phases have been separated (and it was never a good idea anyway). This necessiated changing some choices of characters to be produced, and which would be considered the variant form. The selections were made to match the STIX fonts, and some fancy remapping was done in the MathJax fonts to accommodate that. Should resolve issue #300.

Author: dpvc