Add convert attribute to cameras

for manipulating frames before they are returned by grab, fixes #325
Test frame conversion
Update the docs

Including showing the camera module docstring.
Merge pull request #326 from ufo-kit/grab-convert

Grab convert
Add intensity normalization
Test intensity normalization
Merge pull request #328 from ufo-kit/rescale-image

Normalize image intensities
Fix IPython version check by gevent inputhook
Allow KeyboardInterrupt when gevent is enabled
Enable interrupting parameter accessors

for getters just silently exit and by setters allow the parametrizable to have
_cancel_param method for reverting the setter effect.
closes #330
Make devices abortable

which means bring them to some safe state.
Implement _abort methods in devices
Enable aborting all devices from a concert session
Add abort tests
Implement parameter setting cancellation in motors
Enable interrupting future's join and result
Add cancel_operation to futures for cancel cleanup
Add cancel_operation test
Cleanup after async parameter setter interruption

with proper cleanup.
Update the docs