Break out blocking and exec booleans into setters

[g105b]

Currently there are two boolean flags on the Process::exec function. These should be moved to setters (setBlocking, setExec, for example). This will allow easier refactoring, especially for #9

[g105b]

Closed already: https://github.com/PhpGt/Daemon/blob/4609225cf82a1f13a5f7364870a2b5f52c6a2529/src/Process.php#L163-L165