Multi-echo background documentation edits

[handwerkerd]

Progress for #290

Changes proposed in this pull request:

• Created a new page for the embedded publications spreadsheet rather than just having a link to a google doc buried in the middle of a page
• Put a few more background references and another educational talk into multi-echo.rst
• Corrected. a few quirks that were causing problems with how the documentation was being formatted for ReadTheDocs

Others should take a look at how the spreadsheet renders within ReadTheDocs to see if they think it's ok. It goes a bit beyond the edge of the standard frame, but I think this still looks better than just asking people to go to a separate webpage with the spreadsheet.

I've explained more about the ReadTheDocs warnings in #350 but I fixed some of the low handing fruit in this PR

[codecov]

Codecov Report

Merging #351 into master will not change coverage.
The diff coverage is n/a.

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  Coverage   49.15%   49.15%           
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  Files          39       39           
  Lines        2142     2142           
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  Hits         1053     1053           
  Misses       1089     1089

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[handwerkerd]

This should be a fairly quick review. As @tsalo noted, just run "make html" in the docs directory & you'll be able to see that everything rendered correctly. It would be good if @dowdlelt checked to see if he likes how his spreadsheet of publications is rendering within the documentation. In relation to #350 it would be useful if @jbteves and others also ran "make html" to see what the underlying issue is.

[tsalo]

Everything looks good to me. The table rendering is really cool.

[dowdlelt]

I think having the spreadsheet embedded is great, even if it looks a little funny being so wide. Feel like that allows people to know what they are getting before the click. Loving all the other resources as well.

In this format, it makes me think that there are some improvements to the overall formatting that would make it look even better. I've fallen far behind on updating details (though I've just added another ~10 or so 2019 papers) but I've not given up - Probably try and clean things up a bit before too long.

[jbteves]

This is fantastic, and I love the spreadsheet embedding! I'm not worried about it being perfect because I'm hard pressed to think of any other software that offers such a comprehensive list of related studies anyway, let alone one embedded so conveniently. Fantastic!
However, I did notice that @dowdlelt is still listed as a grad student, and he is actually now a postdoc : - ) so the spreadsheet should be updated accordingly.