Enable `watch` server from arbitrary host about fsharp.formatting

[nojaf]

As mentioned in #925 (comment), I would short term try the --parameters root "/" in watch mode.

Ideal situation would probably be have root be / by default (in future versions) and have a --root flag to easily set this parameter.

I don't know why root has to be localhost for watch mode. I propose to change this and deal with the real problem once it surfaces. We can also play with this during some alphas.

[nojaf]

Ah yes, this rings a bell. Maybe adding --parameters root "" will allow for an empty root and makes things relative but I haven't tested this.

[tymokvo]

Hm, that's a start. But it seems that flag works for build but not for watch. All of the static files generated in tmp/watch are still using absolute URLs to localhost:8901.

[tymokvo]

I think I figured out a patch in #925 . But I'm a little suspicious since there was a whole branch dedicated to preventing a user override of root in watch mode.