This reverts commit 1e6c0860, reversing
changes made to 2c5da944.

The changes to Kwant's Lapack wrappers depend on features from
Scipy 0.16, so it cannot be merged into stable branch, which
depends on Scipy 0.14.

fix pickling on Cython 0.26

See merge request !175

Closes #170

enable PDF documentation builds

See merge request !171

Produce vector graphics, rather than rasterizing,
as rsvg-convert does.

Add the 'unicode-math' package and set the
latex engine to 'xelatex'.

Closes #126.

improve 'attach_lead' docstring

See merge request !170

sympy is installed in the Kwant testing image now.

We can now use Scipy's Cython interface to Lapack, which removes the need for us to explicitly link against blas or lapack ourselves. Also cut down boilerplate by re-arrange the existing Lapack wrappers to use Cython fused types.

Closes #28

See merge request !149

We use Cython's import mechanism to use the the same lapack used
by Scipy, so we no longer need to explicitly link against lapack
or blas.

Closes #166.

There is no point in repeating the docstring in 2 places, though we
leave in the explanation of what this means in the "simplest case", i.e.
lowest modes first, for clarity.

Previously a point defect introduced by an incorrect treatment
of the origin produced erroneous scattering. We also update the text
to reflect the actual magnetic potential used.

Closes #156.

I assume that most people encounter the tutorial example scripts by
reading the documentation, and not by viewing the tutorial subdirectory
of a checked-out Kwant source.

That's the motivation for moving all the manipulations of tutorial
scripts from setup.py to doc/Makefile.  Previously, a successful 'make
html' would require a preceding execution of 'setup.py build_tut'.  Now,
a simple 'make html' is enough.

While at it, I reorganized where the example scripts and their outputs
are stored.  Everything is now in 'doc/source/code' with its three
subdirectories 'download' (to be shown to readers), 'include' (with
include markers), and 'figure' (figure generation & figures).  This
organization is clearer and also makes the generation of figures
separate from the tutorial.

The basic idea remains the same, but should work much better now.  The
difference is that images/example.py.diff is now a patch with complete
context and becomes the authoritative source for both the visible flavor
of an example as well as for its figure-generating variant.  Both
tutorial/example.py and images/example.py are extracted from this file
by 'make html'.  Thanks to the complete context the diffs are quite
readable and may be modified directly.

Alternatively, one may also modify the generated scripts.  When
tutorial/example.py has been modified, it will be patched and saved as
images/example.py.  The patching is done using the tool 'wiggle' that
works much better than 'patch'.  If a conflict occurs, conflict markers
are added to the output file and its dated back to the dawn of time
(i.e. 1970) in order to mark the conflicts as not yet resolved.  After
resolving, 'make html' is simply run again.

Upon a successful execution of the figure-generating script the diff
gets recreated automatically, 'generate-diffs' no longer exists.

These classes used not to have any features beyond
kwant.system.{Finite,Infinite}System, but this is no longer the case.

update the mode ordering documentation as it applies to kwant>=1.3.