Add arguments to state-call
Signal error when no state is found
Add keep property in state structure
Install transient keymap when keep property is non-nil
Remove lexical-binding from prop-line and add an emacs 24 dependence
Re-add missing lexical-binding prop-line
Add ERC state to illustrate the keep property
Fix compilation warnings
Throw error when not implemented
Handle multiple states sharing the same key
Really fix cl-lib dependence
Use functionp instead of atom

Fixes weird behaviour where a lambda is correctly called if not compiled
and saw as an atom as soon as it is compiled :(
Update docstring of state--filter accordingly