Rename class SignalHandler to Signal
Rename class Item to Process
Rename "example.php" to "examples/spawn.php"
Improve signal handling

- Use `declare(ticks = 1)` on constructor;
- Moved the default signal handling definition to method
  `setDefaultHandlers()`;
- Create an example of handling signals.
Implement alarm and create an example of
Force to pass IPC to Process' constructor
Check PID before run PCNTL wait
Implement proccess timeout using pcntl_alarm()
Update spawn exemple
Remove unecessary checking
Merge branch 'develop'