Package signal implements access to incoming signals.
Notify causes package signal to relay incoming signals to c. If no signals are listed, all incoming signals will be relayed to c. Otherwise, just the listed signals will.
Package signal will not block sending to c: the caller must ensure that c has sufficient buffer space to keep up with the expected signal rate. For a channel used for notification of just one signal value, a buffer of size 1 is sufficient.
It is allowed to call Notify multiple times with the same channel: each call expands the set of signals sent to that channel. The only way to remove signals from the set is to call Stop.
It is allowed to call Notify multiple times with different channels and the same signals: each channel receives copies of incoming signals independently.
Stop causes package signal to stop relaying incoming signals to c. It undoes the effect of all prior calls to Notify using c. When Stop returns, it is guaranteed that c will receive no more signals.