use latest jupyter-sphinx and configure thebelab

Closes #306

See merge request kwant/kwant!308

add 'add_peierls_phase' utility function.

See merge request kwant/kwant!300

This function adds a Peierls phase to a Builder

this decorator will be needed in kwant/builder.py in the next
commit.

Modify tutorial to remove warnings.

In pytest v5 the behaviour of str(exc_info) changed. We now
use str(exc_info.value) as the canonical way of obtaining
the exception message.

Closes #304.

Implement Landau level discretization.

See merge request kwant/kwant!295

Tómas authored 5 years ago and Joseph Weston committed 5 years ago

Co-Authored-By: Joseph Weston <joseph@weston.cloud>

Previously when 'attach_lead' would expand a lead unit cell to deal
with greater than nearest-neighbor hoppings it would unset the
conservation law and discrete symmetries of the lead.

Closes #303.

Closes #279.

Closes #214.

Raise a TypeError when site sizes/colors are provided as arrays
and the system to plot is a kwant.Builder.

Closes #293

See merge request kwant/kwant!301

Raise a TypeError when a site size/color is provided as an array
and the system is a kwant.Builder, as the site ordering for the
latter is not well defined. A function should be used instead.

Closes issue #299

Closes issue #300

Convert tutorial building machinery to Jupyter-Sphinx.

Closes #87

See merge request kwant/kwant!296

Currently we just set the default figure size. Matplotlib is
annoying when it comes to setting these default parameters, and we
have to ensure that we set any 'rcParams' in a separate Jupyter cell
and *after* we import pyplot.