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.

Add an FAQ section to the Kwant tutorial that succinctly answers
user questions that have appeared on the mailing list a number of
times.

lowercase FAQ.rst, FAQ.py, etc., give meaningful names to labels,
and stop building an user-visible tutorial/faq.py

Apply pep8 fixes and refactor some sections to be more idiomatic
(e.g. avoiding triple nested loops). Also some minor reorganisation
of the sections to give the text a better flow.

The alleged mode ordering was the opposite of the true ordering.
The true ordering corresponds to "lowest modes first" when there are
no band crossing.

That test fails because the result of the selfenergy callback is used as a
numpy array without a call to asarray.

make 'monomials' preserve order of operators,
remove some unimportant (redundant) tests,
and improve the API of 'monomials', which is
not yet part of the public API.

Closes #135

See merge request !151

Calling "expand" at this point is not required and differs from
sympy behaviour without a good argument for it. Closes #146.

Current behaviour assumed that all generators shall be commutative.
By preserving order of generators we will preserve at least some
information about order they were present in initial formula.
This information is useful e.g. in Landau Levels project. closes #135

"monomials" are not yet a public function. Interface improvment consists of:

- change "*gens" into single argument "gens" with default value "None".
- If left as "None" it reads all symbols present in the given "expression".
- It is also possible to provide "gens" as sequence of strings (symbol names).

Bump required Python version and library dependencies to the
oldest supported ones. With the release of Debian Stretch
the oldest supported platform is Ubuntu 16.04, which has:

+ Python 3.5
+ numpy 0.11.0
+ scipy 0.17.0
+ matplotlib 1.5.1

We are making these changes now in the expectation that we
will not make a new release before 6 months have elapsed, in
line with our policy to support old platforms for 6 months
after they are supplanted.

Closes #31

See merge request !146

Add check for this in setup.py to avoid potentially confusing
tracebacks later.

Remove fixes for unsupported versions of numpy, scipy and matplotlib.

Previously the test suite generated warnings that were swallowed
when pytest was invoked from the command line. Here we enable
printing of warnings generated during testing, and we also
remove the sources of some of those warnings (e.g. using
deprecated APIs).

Closes #131

See merge request !143

The lead does not have connected unit cells and serves no purpose.
We also remove the check for the number of 'collections' in the
resulting plots, as now both 'syst_2d' and 'syst_3d' produce
systems with 2 leads.

This is the only sane behaviour, otherwise we don't know if our
build is misconfigured because 'build.conf' was silently used instead.

Fixes #133.

Older pytest does not have 'warns'.