Sphinxprettysearchresults

25: Adds support for `dirhtml` builder

Fixes 23 *Sphinx: pretty search results* didn't support multiple source suffixes, which was especially problematic for users who combine reStructuredText and Markdown files in their projects.

Fixes 21 Sphinx: pretty search results didn't remove [transitions](http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.htmltransitions).

Fixes 17: If a `templates_path` is set, *Sphinx: pretty search results* threw a `Recursion error`, because it expected a overridable `sourcelink.html` template at a specific index of `app.builder.templates.loaders`. Now, the extension searches in all loaders for `sourcelink.html` and doesn't attempt to override `sourcelink.html` if it can't find this template.

Fixes 14: When rebuilding a Sphinx project without cleaning/removing the build files, the build can fail, because the extension expects that the `_raw_sources` directory doesn't exists.

Previously, the extension would overwrite the source files Sphinx copies to the build result. This is a problem for projects that have the property [html_show_sourcelink](http://www.sphinx-doc.org/en/stable/config.htmlconfval-html_show_sourcelink) activated. This commit fixes the issue by introducing a second directory for "raw" source files. For more details, consider the [README](https://github.com/TimKam/sphinx-pretty-searchresults/blob/master/README.rst).