Child process support

[saghul]

Some sources for inspiration:

• https://docs.python.org/3.6/library/subprocess.html#subprocess.run
• https://docs.python.org/3.6/library/subprocess.html#popen-constructor
• https://nodejs.org/api/child_process.html

Base:

• [x] os.fork
• [x] os.execve
• [x] os.waitpid
• [x] os.getpid
• [x] os.getppid
• [x] os.dup
• [x] os.chdir
• [x] os.setsid

Process module:

• [x] process.daemonize
• [x] process.spawn