Improved deno support

[shreyasminocha]

We currently output a mod.js for deno and an index.d.ts for node. index.d.ts doesn't work with deno because (a) it doesn't have the types for our dependencies bundled, and (b) index.d.ts isn't referenced in mod.js, so deno wouldn't know where to find the types anyway.

Once we figure out the bundling of types for deno, we should also:

• add a section about deno to the readme
• add a deno example
• potentially publish to deno.land/x

Also, mod.js currently includes, bundled-in, all our dependencies. Ideally it would import them.