Use .npmignore to control file inclusion

[50Wliu]

This was superseded by #92.

The 4.0.0 publish only contains 4 files:

npm notice === Tarball Contents ===
npm notice 1.2kB  LICENSE
npm notice 2.5kB  README.md
npm notice 11.3kB SDK.js
npm notice 995B   package.json

I suspect this is because the existing practice has to been to publish from within the bin folder, a strategy that no longer works with the new build process.

To fix that, I've updated the package to support publishing from the root, which will capture all the necessary files.

npm notice === Tarball Contents ===
npm notice 1.2kB  LICENSE
npm notice 2.5kB  README.md
npm notice 2.8kB  SECURITY.md
npm notice 7.8kB  bin/esm/SDK.d.ts
npm notice 8.9kB  bin/esm/SDK.js
npm notice 21.7kB bin/esm/SDK.js.map
npm notice 8.5kB  bin/esm/SDK.min.js
npm notice 7.5kB  bin/esm/XDM.d.ts
npm notice 18.8kB bin/esm/XDM.js
npm notice 39.3kB bin/esm/XDM.js.map
npm notice 5.4kB  bin/esm/XDM.min.js
npm notice 7.8kB  bin/SDK.d.ts
npm notice 11.3kB bin/SDK.js
npm notice 21.9kB bin/SDK.js.map
npm notice 11.1kB bin/SDK.min.js
npm notice 7.5kB  bin/XDM.d.ts
npm notice 22.8kB bin/XDM.js
npm notice 40.7kB bin/XDM.js.map
npm notice 7.5kB  bin/XDM.min.js
npm notice 981B   package.json

Furthermore, I've updated package.json so that people who are using ES modules can actually leverage the new ESM format in 4.0.0.

Fixes #90