additional delimiters / delimiter commands

[manuelbb-upb]

When testing a related issue in #148 I noticed that some common delimiter commands (like \langle) don't work (anymore).

I have added them and enabled the tokenizer to recognize them as arguments for \left and \right.
The symbols < and > have been removed as delimiters (as they are binary relation symbols).

Explicit tests are added for the symbols and commands, and a test based on the dictionary delimiter_commands to check if they work in a group wrapped by \left and \right.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.93%. Comparing base (819bbec) to head (efdbaab).
⚠️ Report is 53 commits behind head on master.

Files with missing lines	Patch %	Lines
src/parser/parser.jl	66.66%	2 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #149      +/-   ##
==========================================
+ Coverage   78.39%   79.93%   +1.54%     
==========================================
  Files          10       10              
  Lines         597      658      +61     
==========================================
+ Hits          468      526      +58     
- Misses        129      132       +3     

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[Kolaru]

Thanks so much for your contributions @manuelbb-upb ! This is an immense work, and it looks truly stellar ✨

I will try to review everything slowly, starting with this one, which seems to be the simplest.

For now, I've merged master into the branch to see if the (new) reference test are passing. If they are, I'll merge the PR

[Kolaru]

This reference test think is nice, showing that you improved things here :D

Everything is therefore good, merging, and thanks again !

[manuelbb-upb]

Thanks for checking :) Some time ago I have merged most of the pull requests into my own development fork and it was indeed a bit fiddly.
I think #150 is easy.
With #147 I am unsure about (internal) naming of functions etc.
#148 needs larger changes, e.g., FontFamily type is changed. Also, italic correction becomes kind of obsolete with #143.
If I can be of any help with merging, please let me know.