Refactor typo away: renderes -> renderers
Provide an empty list as default value for plugins

Otherwise, if you have a config.yaml file and don't specify any plugins in it, beetle will fail because the iterator in cli.py is iterating over None.
Added a 'help' command which display the available commands
PEP8 and Pylint clean up

Removes some unused imports (and the dependency on markdown), plus adds some newlines where PEP8 dictates them
Mention beetle-example project in README file
Fix minor typos in the README
Merge pull request #8 from Tenzer/code-cleanup

PEP8 and Pylint clean up
Merge pull request #10 from Tenzer/mention-example-site

Mention example site in README
Merge pull request #5 from Tenzer/refactor-typo

Refactor typo away: renderes -> renderers
Merge pull request #6 from Tenzer/provide-default-value-for-plugins

Provide an empty list as default value for plugins
Merge pull request #7 from Tenzer/help-output

Added a 'help' command which display the available commands
Added thanks to Jeppe in readme.