Ergonomy

• removed set_state function that was too error prone. Forgetting to call it to pass the state immediately lead to segfault. Instead, state must be passed along with subscribe
• variables can now be directly updated using the update functions, courtesy of Dan Faudemer !
• Methods match and fullmatch that will return true if received frame topics matches with a given topic. Fullmatch also checks for payload type that should match a given type as well