Switch BAT to use Results

[IAlibay]

Fixes #3272
Towards #3261

Changes made in this Pull Request:

• BAT is new in 2.0.0, so it's a direct switch from bat to results.bat.
• Did a bit of cleaning up whilst I was there, including; a misindented code block and added a test.

PR Checklist

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

[pep8speaks]

Hello @IAlibay! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-05-06 21:08:25 UTC

[orbeckst]

lgtm, thanks

[orbeckst]

Technically not needed because bat wasn't released – but I think I said in the past "if it has an issue then list it"... so leave it in

[orbeckst]

I changed the issue text to include CHANGELOG entry

[codecov]

Codecov Report

Merging #3273 (9e60359) into develop (2c714fc) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #3273   +/-   ##
========================================
  Coverage    93.02%   93.02%           
========================================
  Files          172      172           
  Lines        22703    22704    +1     
  Branches      3193     3193           
========================================
+ Hits         21119    21121    +2     
+ Misses        1534     1533    -1     
  Partials        50       50           

Impacted Files	Coverage Δ
package/MDAnalysis/analysis/bat.py	97.57% <100.00%> (+0.62%)	⬆️

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