fix(docs): images, anchors, show html

[levithomason]

1. Add missing images and fix src props
2. Restore example show HTML button
3. Only show example menu on hover
4. Remove anchors from example section headers (examples have direct links)
5. Various example layout tweaks

[codecov-io]

Codecov Report

Merging #1471 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1471   +/-   ##
=======================================
  Coverage   99.74%   99.74%           
=======================================
  Files         141      141           
  Lines        2363     2363           
=======================================
  Hits         2357     2357           
  Misses          6        6

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