Implement encoding and decoding functions

[thomashoneyman]

This PR introduces the encode and decode functions for URIs and for x-www-form-urlencoded. It solves this comment wrt updating libraries to PureScript 0.14.

I've relied on the MDN documentation seen here:

• https://web.archive.org/web/20201206001047/https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent
• https://web.archive.org/web/20201204193427/https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/decodeURIComponent

I haven't yet added tests for these functions, but this PR at least allows us to bikeshed on implementation & naming.

[thomashoneyman]

I can drop the strings dependency if I apply replacements in JavaScript instead of in PureScript (for the *FormURLComponent functions).

[garyb]

I'm not against this. This library already has some non-trivial FFI bindings (well, they're only just non-trivial 😄) so doing it all in the FFI is fine to me.

[thomashoneyman]

Once merged, I can make a release, add this to the 0.14 package set, and then:

1. Deprecate the globals library
2. Update affjax, uri, routing, and form-urlencoded to rely on this library instead of globals
3. Create an issue to replace this library, one day, with an implementation in PureScript that doesn't rely on the FFI so that it can be reused by other backends.

[hdgarrood]

I didn’t realise that the longer term ambition is to have this library written in PureScript with no FFI; in this case I think the name js-uri is actually a bit misleading. Or at least, it will be once that happens.

[thomashoneyman]

I don't think this library should be rewritten in PureScript, just that it would be ideal for some RFC 3896 encoding / decoding to exist which is not written using the FFI.

[JordanMartinez]

I'm pretty sure this is just a stopgap solution so we can get v0.14.0 out the door.

[thomashoneyman]

Unless someone disagrees, once I've added some tests and dropped the strings dependency I'd like to publish this library and use it to complete the 0.14 transition for all contrib libraries. I plan to do that sometime tomorrow unless someone voices dissent before then. Thanks!