Custom router API

[Archmonger]

Description

This PR plays around with the ReactPy-Router's internals to make custom routers possible.

• FixUpdate CompiledRoute.resolve to return a dataclass, not a tuple #38
• FixCreate docs for "Creating a Custom Router" #35

Checklist

Please update this checklist as you complete each item:

• Tests have been developed for bug fixes or new functionality.
• The changelog has been updated, if necessary.
• Documentation has been updated, if necessary.
• GitHub Issues closed by this PR have been linked.

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