Adds a .gitignore

Adds *.pyc files and output/ and cache/ directories to .gitignore.
Updates theme

Updates the pelican-bootstrap3 theme to the latest release (commit
c792fd74c8 from December, 2).
Removes HTML escaping

In .py files there is no need to use HTML escape characters, since
you're using unicode strings.
Merge pull request #1 from magnunleno/pelican

Simple improvements