Document \mathdefault{} and \mathregular{} and the new mathtext.default rcParam.
Merge branch 'mathdefault'
fixed a mincnt problem with hexbin
added support for mincnt to hexbin
fixed a bug in the nsorted changes
Fix typo.
default to draw_idle in draw_if_interactive if it is supported
fix another typo
use default css, fix typo in installation guide.
