#7 Stretchy symbol from font file

[Jérôme Joslet]

Enable pMML2SVG to find the glyph that best fit the gap that an operator has to fill while stretching by browsing a list of font that contains different size for the same glyph.

For example, the bracket has different size depending on the font family that is used. STIXSize2 has a bigger bracket than STIXSize1, STIXSize3 has a bigger bracket than STIXSize2, etc.

This improvement can be done by adding all these font in the font file list and by implementing a simple algorithm (in the formatting mode) that will retrieve the font family that have a glyph that best fit the gap. This font family has to be alone when drawing the glyph in the drawing mode to draw the right glyph.

The render will be better with this improvement.