feat: add rollup bundler, remove submodules

[Polybius93]

This pull request adds Rollup dev dependencies to bundle the dist properly, enabling the option to import everything from one file. To achieve this, submodules were removed. Additionally, tiny-secpk256k1was replaced by @bitcoinlabs/tiny-secpk256k1. It also adds Buffer as a dependency, ensuring it is loadable in a browser context as a script.

[sosaucily]

Very cool, this is a great upgrade. Did you try to get the index.js file to be named something other than index.js? Or want to try that later? I suppose even if it's called index.js here, it can still be uploaded to the CDN with another name.

Also, just checking that this still works as an npm package?

[Polybius93]

Very cool, this is a great upgrade. Did you try to get the index.js file to be named something other than index.js? Or want to try that later? I suppose even if it's called index.js here, it can still be uploaded to the CDN with another name.

Also, just checking that this still works as an npm package?

Thanks! I didn't try to rename it, I didn't see any other example where the entry point is named differently. If you would like to have that modification, I can try it, but generally I don't see any reason to do that. I guess on the CDN we can call it however we want, but it won't be just a file name but a full link, so it won't confusing with other index.js files. I have tried it locally, it worked properly, but I haven't published it yet, so I didn't try it as a package, but I can before we merge it.

[sosaucily]

We are using an API service now, instead of this package rolled-up, so this is no-longer needed