Change CHARMM selection syntax page

[IAlibay]

Fixes #2971

Changes made in this Pull Request:

• swaps the old CHARMM selection syntax page to new one.

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

[lilyminium]

Ideally this would go into master as well, do we have a backports PR going on?

[IAlibay]

Ideally this would go into master as well, do we have a backports PR going on?

I was just looking for it, but I think the last one got merged, I'll raise a separate PR.

[codecov]

Codecov Report

Merging #2972 into develop will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #2972      +/-   ##
===========================================
- Coverage    93.05%   93.03%   -0.02%     
===========================================
  Files          186      186              
  Lines        24609    24542      -67     
  Branches      3187     3187              
===========================================
- Hits         22900    22833      -67     
  Misses        1661     1661              
  Partials        48       48              

Impacted Files	Coverage Δ
auxiliary/base.py	90.75% <0.00%> (-0.57%)	⬇️
coordinates/base.py	94.85% <0.00%> (-0.27%)	⬇️
util.py	89.39% <0.00%> (-0.08%)	⬇️

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