* Use `code-block` to see if that renders differently

See https://groups.google.com/forum/#!topic/django-oscar/-F1rEUX-RZA

To avoid confusion.

Fixes #429

Fixes #310

Update makefile and docs to reflect this change.

Fix requirements_oscar.{py,txt} file extension in tutorial.

This makes it much easier to get started when contributing.  The docs
are also updated.

This makes it much easier to get started when contributing.  The docs
are also updated.

This avoids conflicts with other libraries that use the same trick for
extending templates.