Fluent interface to catch exceptions

[thekid]

Example

Sequence::of($import)
  ->peek(function($record) { Console::write($record['name']); })
  ->map(function($record) {
    $existing= $this->database->lookup($record['name']);
    return $this->database->replace($existing, $record);
  })
  ->catch(function($e) { $e->printStackTrace(); })
  ->peek(function($id) { Console::writeLine(' -> #', $id); )
  ->each()
;

BC break

⚠️ Sequence::$EMPTY needs to b rewritten as Sequence::empty().

Performance

This pull request introduces wide-ranging implementation changes, which also have a slight performance hit:

# [feature/catch]
$ xp -m ../measure/ measure -n 1000 Operations
counting: 1000 iteration(s), 1.159 seconds, result= 10000
collecting: 1000 iteration(s), 2.067 seconds, result= 10000

# [master]
$ xp -m ../measure/ measure -n 1000 Operations
counting: 1000 iteration(s), 1.013 seconds, result= 10000
collecting: 1000 iteration(s), 1.857 seconds, result= 10000

See also http://reactivex.io/documentation/operators/catch.html and #30

[thekid]

Think about wrapping this in a lang.Throwabe.

[thekid]

#30 seems to cover more usecases