Add mutable access to Message fields

[leshow]

closes: #1117

[codecov]

Codecov Report

Merging #1118 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1118   +/-   ##
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  Coverage   85.00%   85.00%           
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  Files         125      125           
  Lines       13377    13377           
=======================================
  Hits        11370    11370           
  Misses       2007     2007           

[leshow]

I left the return type as &mut Vec, but a mutable slice is also an option, let me know if you have a preference.

[bluejekyll]

If you want to be able to insert new Records into the answers or other sections, then I think it needs to be a &mut Vec, right? Otherwise you would be limited to changing existing entries, right?

[leshow]

The particular use case was modifying existing Records in answers, so either type would work for me. I've left it as &mut Vec though which is the most "open" option, if you're okay with that change.

[bluejekyll]

The only concern to think about is that we are exposing the internal data structure of the Message. I think I'm ok with this, but I want to think about it for a little bit.

[bluejekyll]

Ok, let's merge this, as-is, can always revisit in the future.

[bluejekyll]

Thanks for the PR!

[leshow]

Thank you!