Added test exposing the bug in issue #23
split the Viewlet.call() method
the acctual calling of the viewlet function is now exec. by Viewlet._call() aswell as all the cache handling
and the logic left in call() is only handling the rendering of context viewlets
this to enable refresh() to only trigger whats necessary
Changed Viewlet.refresh() to call self._call() instead of self.call()
Refactored a test affected by the refresh changes
flake8 fixes
version bump
Merge pull request #24 from gardeman/refresh-refectoring

Fixes #23