Improve Unicode docs

[ronkok]

Restore a feature to the function support page in which the Unicode Mathematical Alphanumeric Symbols section renders its letters in the relevant font.

[codecov]

Codecov Report

Merging #1533 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1533   +/-   ##
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  Coverage    84.1%   84.1%           
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  Files          79      79           
  Lines        4561    4561           
  Branches      804     804           
======================================
  Hits         3836    3836           
  Misses        630     630           
  Partials       95      95

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[kevinbarabash]

@ronkok thanks for adding this back in. Fractur and Double-struck aren't fully supported. Maybe we should show only the supported character ranges for those type faces.

[ronkok]

@kevinbarabash Thanks for the note. In Fractur and blackboard-bold, we actually do have the range that the table indicates. But we have it only in math mode. A few of the characters are not supported in text mode. So I had to change how the table calls them.

Also, I've found a bug in sans-serif bold and with some numerals. I'll fix it and turn in a PR after #1534 lands.