make showing code examples in the tutorial text robust

.gitignore

MANIFEST.in

doc/Makefile

doc/source/images/generate-diffs.sh

doc/source/tutorial/1-quantum_wire.py

doc/source/tutorial/1-quantum_wire_revisited.py

doc/source/tutorial/2-ab_ring.py

doc/source/tutorial/2-quantum_well.py

doc/source/tutorial/2-spin_orbit.py

doc/source/tutorial/3-band_structure.py

doc/source/tutorial/3-closed_system.py

doc/source/tutorial/4-graphene.py

doc/source/tutorial/5-superconductor_band_structure.py

doc/source/tutorial/5-superconductor_transport.py

doc/source/tutorial/README

doc/source/tutorial/tutorial1.rst

doc/source/tutorial/tutorial2.rst

doc/source/tutorial/tutorial3.rst

doc/source/tutorial/tutorial4.rst

doc/source/tutorial/tutorial5.rst