Fix child process docs

Fix a number of outright errors in child process documentation, as well as improve the general readability of it by using hyperlinks, documenting defaults, ordering the docs consistently, etc.
Apparently not: https://gist.github.com/anonymous/1073848fbefb8c3a32e7 doesn't work.

@piscisaureus @orangemocha , child_process allows creating of pipes for fds larger than 2, is there any way to use them, or are pipes other than for stdio not usefully supported on Windows?