Build and publish an npm package from graphman

[nohehf]

Deno has the capability to be exported as an npm package, which would allow GraphMan to be used as a node module (for now it's only programmatically usable from deno). See: https://deno.land/manual@v1.25.4/node/dnt & https://github.com/denoland/dnt . This needs a little reflection and testing to be done right, but it could be included in a CI at the end to build and deploy new versions when a new tag is added.