samd: Add some documentation for the extended samd port.

[robert-hh]

Matching PR #8704. It consists of the basic introduction, a quickref document and a pinout document, showing, which MCU device is accessible at which board pin. I hope the work is not futile.

[codecov-commenter]

Codecov Report

Merging #8798 (13bc669) into master (6519b1b) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #8798   +/-   ##
=======================================
  Coverage   98.31%   98.31%           
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  Files         157      157           
  Lines       20349    20349           
=======================================
  Hits        20006    20006           
  Misses        343      343           

Impacted Files	Coverage Δ
ports/unix/moduos.c	18.91% <0.00%> (ø)

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[dpgeorge]

Please can you make sure the docs CI passes.

[robert-hh]

Done. It was the second-to-last commit, missing indents at a code block.

[robert-hh]

Hello @dpgeorge The new commit removes the vertical bars in the file. Once you merge the samd_improve branch, the pinout file has to be update. I have prepared that already, so it can be swapped in any time.

[dpgeorge]

Squashed all commits into one (most were fixes/improvements) and merged in 11910e2fa1c8f5dc76cbc90598ff81526d1f6312 with some minor formatting fixes.

Thank you very much!

[robert-hh]

Thanks. Yes, the commits were all around that single topic "documentation". The samd port looks now pretty complete. There is little left. Since most boards do not have a on-board SD adapter, I skipped I2S support. dac timed and adc timed are there as a "poor man's audio interface", so you can play and record short audio snippets at moderate quality. The mcu's have hardware support for position decoder and counters, but since there is no common approach to that yet, it has to wait. b.t.w.: There is a PR21 open at the micropython-media repository for the missing pictures. But that's not urgent at all.

[andypiper]

Amazing work here. Thanks @robert-hh 🙂