[Live site affected] Sphinx-build to html shows 10 warnings (inc. 2 errors)

## Sphinx-build warnings (inc. 2 errors)
```bash
$ make html
sphinx-build -b html -d _build/doctrees   . _build/html
Making output directory...
Running Sphinx v1.2.3
loading pickled environment... failed: [Errno 2] No such file or directory: '/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/_build/doctrees/environment.pickle'
building [html]: targets for 28 source files that are out of date
updating environment: 28 added, 0 changed, 0 removed
reading sources... [100%] index                                                                                                                                              
/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/chapters/bing_search.rst:142: ERROR: Unexpected indentation.
/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/chapters/login_redux.rst:65: WARNING: Explicit markup ends without a blank line; unexpected unindent.
/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/chapters/models.rst:395: WARNING: Inline literal start-string without end-string.
/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/chapters/models_templates.rst:147: ERROR: Error in "code-block" directive:
1 argument(s) required, 0 supplied.

.. code-block::

        $ python manage.py makemigrations rango
        $ python manage.py migrate
/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/chapters/requirements.rst:371: WARNING: Inline literal start-string without end-string.
/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/chapters/requirements.rst:378: WARNING: Inline literal start-string without end-string.
looking for now-outdated files... none found
pickling environment... done
checking consistency... /home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/chapters/acknowledgements.rst:: WARNING: document isn't included in any toctree
/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/chapters/javascript.rst:: WARNING: document isn't included in any toctree
/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/chapters/virtual.rst:: WARNING: document isn't included in any toctree
done
preparing documents... done
writing output... [100%] index                                                                                                                                               
writing additional files... genindex search
copying images... [100%] chapters/../images/rango-register-form.png                                                                                                          
copying static files... WARNING: html_static_path entry '/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/_static' does not exist
done
copying extra files... done
dumping search index... done
dumping object inventory... done
build succeeded, 10 warnings.

Build finished. The HTML pages are in _build/html.
```

## Resultant problems (present on live website)
http://www.tangowithdjango.com/book17/chapters/bing_search.html:
* The hint bullet point is indented more than the other bullet points

http://www.tangowithdjango.com/book17/chapters/login_redux.html:
* The closing bracket is not shown within the code block

http://www.tangowithdjango.com/book17/chapters/models.html:
* Corrupted output: \`\`IntegerField\`\`s

http://www.tangowithdjango.com/book17/chapters/models_templates.html:
* Code block missing!  Should show:
```python
	$ python manage.py makemigrations rango
	$ python manage.py migrate
```

http://www.tangowithdjango.com/book17/chapters/requirements.html:
* Corrupted output: \`\`lsvirtualenv’‘
* Corrupted output: \`\`pip list’’

## Sphinx-build warnings after fixes applied
```sh
$ make html
sphinx-build -b html -d _build/doctrees   . _build/html
Running Sphinx v1.2.3
loading pickled environment... done
building [html]: targets for 6 source files that are out of date
updating environment: 0 added, 6 changed, 0 removed
reading sources... [100%] index                                                                                                                                              
looking for now-outdated files... 3 found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] index                                                                                                                                               
writing additional files... genindex search
copying images... [100%] chapters/../images/bing-explore.png                                                                                                                 
copying static files... WARNING: html_static_path entry '/home/imran/Downloads/TangoWithDjango/tango_with_django_book/17/_static' does not exist
done
copying extra files... done
dumping search index... done
dumping object inventory... done
build succeeded, 1 warning.

Build finished. The HTML pages are in _build/html.
```

## Notes
* I've separated the changes into two commits:
 * The first commit is the important one which has a detrimental affect to the live site
 * The second commit is almost definitely unnecessary, since the pages that are missing from index.rst are of no consequence