Distribute as a single NPM package

[klntsky]

browser field in a package.json allows to point the bundler to an alternative source specifically when bundling for the browser.

Therefore, CSL could be distributed as a single NPM package instead of -nodejs and -browser versions.

For example, we vendored CSL and did exactly that:

https://www.npmjs.com/package/@mlabs-haskell/cardano-serialization-lib-gc - see source package.json

[lisicky]

Hi @klntsky ! Thanks it's good idea to consider merging CSL into one package at least for nodejs and browser version. It's not priority for us now, but we will consider it.
cc @vsubhuman