[feature] Add CLI for using via `npx`

[ilyaigpetrov]

I would like to run npx merge ./foo.json ./bar.json or similar from my project build scripts.

[ilyaigpetrov]

I've made some early work and want it to be reviewed by the repo maintainers: see https://github.com/ilyaigpetrov/merge.
I need your guidance. I want to deliver code that will be easier for you to maintain. E.g. I need guidance in such questions as should I use TypeScript, es modules, where to output the executable script, etc.

[ilyaigpetrov]

Added a user-scoped package on npmjs so you can test like this:

npx @ilyaigpetrov/merge objA.json objB.json

Published from https://github.com/ilyaigpetrov/merge/tree/npm-scoped to https://www.npmjs.com/package/@ilyaigpetrov/merge.