Discovery of peer executors

[Nokome Bentley]

I propose to reinstate the files based Executor registration and discovery mechanism that we had previously. This time around however we will keep it simpler by using STDIO where possible (e.g

Previously the approach was...Executors (f.k.a. Hosts) register() themselves by creating a JSON file containing their "manifest". For example, the Python host created the following ~/.stencila/hosts/py.json file here

{
 "id": "py-host-6494cd21-0424-4dda-a407-8e5d2957d652", 
 "stencila": {
  "package": "py", 
  "version": "0.0.0"
 }, 
 "spawn": [
  "/usr/bin/python", 
  "-m", 
  "stencila", 
  "spawn"
 ], 
 "environs": [
  {
   "version": null, 
   "id": "local", 
   "name": "local"
  }
 ], 
 "types": {
  "SqliteContext": {
   "client": "ContextHttpClient", 
   "name": "SqliteContext"
  }, 
  "PythonContext": {
   "client": "ContextHttpClient", 
   "name": "PythonContext"
  }
 }
}

The Node Host scanned the relevant directory for those JSON files to discover peers that it could then spawn in response to client requests for alternative types of execution contexts.

In this iteration, we would still need the spawn property, but instead of types would have capabilities ala this.

[Stencila CI]

🎉 This issue has been resolved in version 1.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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