New doc design

[benjeffery]

Using new tskit-book-theme

The only question I have is whether this is acceptable:

[codecov]

Codecov Report

Merging #2102 (27d54ab) into main (e08b94f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2102   +/-   ##
=======================================
  Coverage   91.32%   91.32%           
=======================================
  Files          20       20           
  Lines       10889    10889           
  Branches     2270     2270           
=======================================
  Hits         9944     9944           
  Misses        516      516           
  Partials      429      429           

Flag	Coverage Δ
C	91.32% <ø> (ø)
python	98.74% <ø> (ø)

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[jeromekelleher]

What does the current viz look like?

[benjeffery]

[jeromekelleher]

Thanks - LGTM!