This is the correct lexer for interactive console sessions, according to
<http://pygments.org/docs/lexers/>. This does require command lines to
be prefixed with `$`, otherwise they are interpreted as the output of a
command. It highlights the command nicely, including environment
variables, strings, and comments.
All `.. code::` instances have been changed to use `.. code-block::`,
and have been properly formatted. The syntax names have been normalised,
so all django templates use the `html+django` syntax, shell commands use
`sh`, and plain text uses `text`.
