Add support for URL rewriting

Provide "pretty" URLS without .html
Make fingerprinting optional
Do not rewrite URLS for index pages
Added an if_current_page template tag
Use _url instead of path for URLs
Move page context parser + update tests

The context parser should not run on non-HTML files, as this breaks
non-empty robots.txt
Add extra checks in fingerprinting tests
Removed skeleton.py
Refactored utils
Replaced .paths with attributes
Add a compabitibility layer for site.paths
Add cactus.utils to the package list
Added tests for existing plugin loader
Add a new plugin loader
Added a plugin manager to make plugin calls
Added tests to ensure we call plugins
Merge branch 'new-plugins'
Warn when config can't be loaded
Make optimization a configuration variable
Updated readme