"send on closed channel" panics due to incorrect 'Close' method implementation

[antage]

See #16 as example.
We should ensure all goroutines are exited before close all control channels and other stuff.

[flyingmutant]

IMO #18 is a correct approach. What do you think?

[antage]

#18 hides the problem only.
I think a time for big refactoring has come.