Properly convert latex expressions

[pacjo]

Since anki can display latex in [$] and [$$] tags, it would be nice to convert normal markdown latex expressions into anki style ones.

something like:

Fermi-Dirac function:

$$f_{ED}(E) = \frac{1}{1 + \exp{(\frac{E - E_F}{kT})}}$$

could change into:

Fermi-Dirac function:

[$$]f_{ED}(E) = \frac{1}{1 + \exp{(\frac{E - E_F}{kT})}}[/$$]

also stuff inside latex expression shouldn't be parsed as markdown, since something like this:

$$E_i - E_F = kT \ln{\frac{N_A}{n_i}}$$

is converted by the addon to have underline between the underscores.