consistent spelling
Typo
Rename requirements/py25 to py25.txt

For consistency, per Julen's recommendation
Add JSON syntax highlighting to docs

Particularly useful is the red-outlined display of any invalid JSON;
you can see an example by reverting api_translation_project.rst to
the version before this commit (at first I couldn't understand why
the syntax highlighting was so ugly - until I realized that none
of the keys were properly quoted).
Use .. code-block:: only

Don't use trailing :: on previous paragraph and .. code-block:: too;
that just puts the .. code-block:: into a code block and leaves
the actual code block with default formatting.  Remember that the
.. code-block:: bash or whatever *has* a :: so another is unneeded.
Fix broken :ref:s in docs

You can't just :ref: to arbitrary sections in Django docs, the target has
to be in the objects inventory (unless there is an internal reference, it
probably isn't there).  Use |text reference|_ workaround to make "ref-like"
hyperlinks.

Even if something is in the objects inventory, it might have a different
role, than ref - e.g. use :djadmin: for references to Django manage.py
commands (and you may have to add the role to pootle_docs.py extension).
Document migrate command, and the need for it

This fixes missing internal :ref: to commands#migrate as well.