doc: update user guide & Pages deploy

[imrn99]

Structure change:

roughly, the deploy goes from this:

deploy -----> userguide -----> rustdoc

to this:

deploy -----> index --+--> userguide
                      |
                      +--> rustdoc 

Content update

• add kernel pages for DVR (wip), edge splits and triangulation functions
• update grisubal page with the new precompute step
• update content about workspace members
• clean up dead links, empty pages, etc.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.29%. Comparing base (fdb2ed9) to head (4d2ff14).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #217   +/-   ##
=======================================
  Coverage   75.29%   75.29%           
=======================================
  Files          41       41           
  Lines        6376     6376           
=======================================
  Hits         4801     4801           
  Misses       1575     1575           

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