Add support for Cashaddress URI

[yashasvi-ranawat]

Adds support for parsing and generating CashAddress URIs.

[yashasvi-ranawat]

I simplified the uri parsing and generation, uses urllib which makes it quite robust.

I added some simple documentation in dev guides. Is there any other place the documentation should be added?

PS: This also adds the cashaddress class Address, although that doesn't have any docs. I think I'd leave it at that, and wait for cashtokens merge. Otherwise the rebase will be quite messy.

[merc1er]

I added some simple documentation in dev guides. Is there any other place the documentation should be added?

I think that should do. I will build the site and see if that's enough.

[merc1er]

Seems like there's only one mention of URI in the changelog:

It should probably have its own short page with a couple examples, a bit like this: https://bitcash.dev/guide/keys.html#formats.

[yashasvi-ranawat]

It should probably have its own short page with a couple examples, a bit like this: https://bitcash.dev/guide/keys.html#formats.

I added CashAddr as a new page. It also describes the URI. How does that look?