CHARMM selection syntax link no longer works

## Expected behavior ##

All links work.

## Actual behavior ##

The selection syntax link present in the following no longer works: https://docs.mdanalysis.org/1.0.0/documentation_pages/selections.html

I believe the latest version of that page should now be: https://www.charmm.org/charmm/documentation/by-version/c45b1/select.html

## Current version of MDAnalysis ##

Current develop
