Added comments for new routines in qho.

Added comments for psi_3d_cartesian and psi_3d_spherical.
Moved tutorials folder into docs.

/examples -> /docs/tutorials.
Added basic jinja template for ipynb -> rst.

The default generator bundled with nbconvert didn't work very well when
including generated rst files into sphinx.

They now work (just about, with a bunch of warnings). This is definitely
something that should be revisited.
Added tutorials to main documentation.