Separate Reach language server into a different repo

[ericglau]

Currently this repo has two projects:
https://github.com/reach-sh/reach-ide/tree/master/server - which is the Reach language server
https://github.com/reach-sh/reach-ide/tree/master/client - which is the VS Code client that uses the Reach language server

It would be useful to separate code for the Reach language server into a different GitHub repo where it can be published separately as an npm package. Then the VS Code client and any other language client (such as for Vim or Sublime) can just pull it in as an npm dependency.

(It may not be strictly necessary to use a different repo -- the main suggestion here is to publish the server as an npm package. But separating the repos could make it cleaner since VS Code will just be one of the clients.)

@chrisnevers Any thoughts on this?