Fixed #63 - `use_directory_urls` option has no effect.

- The `use_directory_urls` option is now passed forward to the
SiteNavigation object in order to correctly generate links to the
target file when needed.
- The post-processing of the HTML generated by converting from Markdown
now takes the `use_directory_urls` option passed to the SiteNavigation
object into account when changing anchor targets.
- The dev server mode (mkdocs serve) still ignores the
`use_directory_urls` option in order to have user-friendly URLs.
- There is a new test case for post-processing converted Markdown when
  `use_directory_urls` is `False`.
Fixes #65 - Links to other files within documentation are broken on Python 2.6

There was a bug in `posixpath.relpath()` in this version of Python. The
bug was worked around by a verification of the corner case were the
`start` argument is the root directory.
Fixes indentation issues which caused lint errors.

Those errors were causing the `runtests` script to fail.
Fixes location of static assets.

The previous commit made `base_url` incorrectly empty.
Improve whitespace around css and script tags
Remove reference to the `config` variable in the template files
Add support for extra_css and extra_javascript in all the themes
Avoid repeated overwrites of config['extra_*']

Fixes #133
Merge pull request #136 from jimporter/config-var

Remove reference to the `config` variable in the template files for custom themes
Merge pull request #90 from jimporter/extra-css

Add support for extra_css and extra_javascript in all the themes
Merge pull request #134 from dnrce/bug/133-wrong-extra-media-paths

Avoid repeated overwrites of config['extra_*']
Merge pull request #135 from dnrce/extra-media-whitespace

Improve whitespace around css and script tags
Use Tox to run the tests on Travis

Rather than repeating the steps in the Travis config, use Travis to run
tox. This has the added benifit of verifying the setup.py install into a
virtualenv.
Removed flake8 exclusion that wasn't needed
Merge pull request #125 from d0ugal/travis-updates

Use Tox to run the tests on Travis
Added links to Python and pip.
Show coverage for the docs building
Merge pull request #64 from thiagomael/master

Fixed issue #63 - `use_directory_urls` option has no effect.
Fix a typo in the use_directory_urls config name
Verify that parents isn't empty before popping

If the first iteration of the loop isn't a match then parents will be an
empty list.