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
Merge branch 'master' into exceptions

* master:
  Fix minor typos in the README
  Mention beetle-example project in README file
  PEP8 and Pylint clean up
  Added a 'help' command which display the available commands
  Provide an empty list as default value for plugins
  Refactor typo away: renderes -> renderers

Conflicts:
	beetle/builder.py
Added renderer exceptions.
Added NoUrlError.
Renamed error.
Allow the BeetleError class to take a page object as an argument
Add the page which gives the error to the exceptions
Include the file system path in page object

This makes it easier to give some useful error messages to the user in case of an error