Fill gaps in documentation

[justsmth]

Description of changes:

• Update docs for as_ref functions of keys to indicate the encoding being used.
• Update User Guide now that Ninja is no longer required for Windows/ARM64 builds.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.83%. Comparing base (c358484) to head (7cac88a).
Report is 41 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #465      +/-   ##
==========================================
- Coverage   95.80%   92.83%   -2.97%     
==========================================
  Files          61       62       +1     
  Lines        8143     8626     +483     
  Branches        0     8626    +8626     
==========================================
+ Hits         7801     8008     +207     
- Misses        342      362      +20     
- Partials        0      256     +256     

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