Stop exporting deprecated functions.

[korsbo]

Shorthands such as latexalign, mdtable, etc., which can be accessed via latexify(x; env=:align), ect., will be removed from the public API and should not be exported. Removing them allows for a simpler API and for internal updates without major releases.

This will be breaking and I can't think of a good way of signalling this deprecation to users without having to rename the functions internally (which I don't want to do). If I can't think of anything better, there will therefore be a silent removal of the exports at the release of 1.0.