change exception
Merge pull request #4184 from qunox/changeexception

change exception
improve purge message
Merge pull request #4186 from qunox/purgeimprove

improve purge message
Improve checkwrite messages to user.
introducing crab remake
Merge pull request #4178 from qunox/remake

introducing crab remake
Merge pull request #4185 from AndresTanasijczuk/checkwrite

Improve checkwrite messages to user.
Update checkwrite responsability message
alpha release of crabclient library api