Add handlers for read, update, and delete to CREATE_YOUR_FIRST_EXTENSION doc

[dbwiddis]

Description

Updates CREATE_YOUR_FIRST_EXTENSION with the RUD part of CRUD (and a better C example). Also fixes the internal links broken in earlier reviews.

Please merge #827 (and then rebase this PR) prior to merging this PR, as this builds on updates from that PR to Named Routes.

Reference project implementing this, with the code tested: https://github.com/dbwiddis/CRUDExtension

Issues Resolved

Part of #836 (Documentation)

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[dbwiddis]

A couple of comments, mainly making the document more user-centric. Thanks!

Thanks! Can you tell I spent way too long in academia where "we" is the standard? :)

[kolchfa-aws]

Yes, "we" when we're doing an experiment, and "you" when you want the user to do something :)

[owaiskazi19]

@kolchfa-aws @natebower looks good to you before we merge the changes in?

[kolchfa-aws]

LGTM 😄