Remove `fs` dependency to simplify web bundling

[streamich]

This change removes fs dependency which greatly simplifies bundling of this package for web. Should have no effect on Node.js users.

[mafintosh]

Constants are platform dependent. Have you tried bundling with latest? It works fine for me due to the browser field

[mafintosh]

Feel free to open an issue if not

[streamich]

Ah, I totally missed that they can be different per platform, sorry about that.

For me the browser field causes problems, I'm bundling with Webpack and overwriting the fs module with Webpack's resolve.fallback feature. When the browser.fs = false field is present it imports the fs module as empty object:

When I remove the browser field, it rewrites the fs module with what ever I specify as expected.

[streamich]

After some searching found this:

The empty object is what causes the problems, at least for me, it results into constants being undefined, and once retrieving some constant it throws.