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.
Add process coroutine filter

which takes a callable, applies it and forwards the data.
Test process filter
Merge pull request #324 from ufo-kit/generic-coroutine

Generic coroutine
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 greenlet inputhook
Allow ctrl-c when gevent is enabled
Enable interrupting parameter setting

by allowing the parametrizable to have _cancel_param method.
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 gevent futures killing on ctrl-c
Add cancel_operation to futures for cleanup