Add fork method - fixes #65

[SamVerschueren]

It's a start for the execa.fork method. Still need some extra work though but would like some feedback at the initial approach.

One thing I noticed with the stdio option of the original child_process.fork method is that it looks like it ignores the option whenever it's a string. So passing ignore to stdio results in [0, 1, 2, 'ipc']. Even passing stdio: 'foo' results in the same behaviour.

Fixes #65

[SamVerschueren]

I expanded the functionality in the latest commit. Something I missed in the first place is that the first argument of .fork() is the modulePath to a JavaScript file while the first argument of spawn is the command. So currently, I implemented it the exact same way. Not sure if we want to improve this?

[SamVerschueren]

I was thinking this through once again. Actually I don't like an extra method, it just confuses people. If you google for it, a lot of SO posts can be found regarding fork Vs. spawn Vs. execFile. So maybe it would be better if we just add an extra option to the default execa method, something like ipc: true which would always set the 4th argument of the stdio array to ipc. Just a suggestion, but I think it's worth a discussions.

// @kevva @jfmengels @jamestalmage

[sindresorhus]

@SamVerschueren It's not just the IPC though, it also spawns the Node.js binary only, so it's a bit different from execa(). How about execa.node()? Is that clear enough?

[SamVerschueren]

Totally missed this one :).

How about execa.node()? Is that clear enough?

It's clear that it only spawns the node binary, but it's not clear that it opens an IPC channel. What we could do however, is adding an option to execa.node() like I suggested in my previous post, ipc: true to make it explicit. So using execa.node() would just work the same way as execa('node'). Setting ipc: true would add the IPC channel.

[sindresorhus]

Even if it's not clear from just seeing the method, we could make it clear in the docs about the behavior. I don't see the point of a .node() method if I have to set ipc: true manually. Then execa('node') is just as short.

[sindresorhus]

Closing this to clean up open stale PRs.