Add HTTP handlers

[markuswustenberg]

• GET a message
• POST a message
• PUT a message (updates it, right now just to extend the timeout)
• DELETE a message

Fixes #5

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 55.55556% with 32 lines in your changes are missing coverage. Please review.

Project coverage is 76.84%. Comparing base (908bf5d) to head (5bdcbbf).

:exclamation: Current head 5bdcbbf differs from pull request most recent head 59433ae. Consider uploading reports for the commit 59433ae to get more accurate results

Files	Patch %	Lines
http/http.go	55.55%	24 Missing and 8 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #16 +/- ## =========================================== - Coverage 88.54% 76.84% -11.71% =========================================== Files 1 2 +1 Lines 131 203 +72 =========================================== + Hits 116 156 +40 - Misses 11 35 +24 - Partials 4 12 +8 ```

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