Use math mode for TeX rendered ticks

[astrozot]

The ticks rendered using TeX mode (usetex = True in the matplotlib rcParams) have a formatting that does not comply with the standard way one should write numbers. In particular, negative numbers (for example, negative latitudes) should use a longer minus sign. The consistent way of doing this would be to use math mode for these labels: so write for example $-8$ instead of just -8.

In general, it would be nice to have a major control on the way labels are printed. I imagine this is already possible somehow, but could not find a way of doing it (for example, putting dollars in a set_major_formatter does not work...).