Allow configuration of static URL.
Merge branch 'master' of github.com:oddbird/gurtel

* 'master' of github.com:oddbird/gurtel:
  Improve handling of default middleware and context processors.
  Change redirect_if to decorate functions, not app methods.
  Bump to version 0.6.
  Add MapDispatcher and finish refactoring GurtelApp.
  Store assets dir and url on AssetHandler directly.
  Add AssetHandler.
  Add flash context processor.
  Test (and fix) TemplateRenderer's asset handling.
  Extract TemplateRenderer, AssetHandler, and configure_logging from GurtelApp.
  Implement app-level middlewares as single function.

Conflicts:
	gurtel/app.py
Bump version to 0.6.1.