[WIP] Add support for special commands in favorite queries.

[tsroten]

Description

This makes it so your favorite queries can use special commands. For example, you might have a regular export or command you run that should use a particular table format.
\T csv; \once /path/to/export/file.csv; select * from tables limit 5; \T ascii;

Or
\T tsv; pager vim -; select 1, 2, 3; \T ascii; pager less;

NOTE: There is still some weird behavior here with the headers and status of the results being outputted more than once.

• Fix issue where some query headers are outputted twice.
• Add tests.

Checklist

• I've added this contribution to the changelog.md.
• I've added my name to the AUTHORS file (or it's already there).

[codecov-io]

Codecov Report

Merging #600 into master will increase coverage by 0.01%.
The diff coverage is 87.5%.

@@            Coverage Diff             @@
##           master     #600      +/-   ##
==========================================
+ Coverage   77.88%   77.89%   +0.01%     
==========================================
  Files          25       25              
  Lines        2401     2407       +6     
==========================================
+ Hits         1870     1875       +5     
- Misses        531      532       +1

Impacted Files	Coverage Δ
mycli/packages/special/iocommands.py	88.8% <87.5%> (-0.13%)	⬇️

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