added triplet interactions: ring-exchange and spin-chirality coupling

[SpiritSuperUser]

[coveralls]

Coverage remained the same at 79.821% when pulling 263a7ec3ac6f790a4277c38253c8882a70926efb on SpiritSuperUser:triplet into b5351e570688cc5662156d249c965f3f147a9e20 on spirit-code:develop.

[codecov[bot]]

Codecov Report

Merging #462 (263a7ec) into develop (b5351e5) will decrease coverage by 0.72%. The diff coverage is 8.96%.

@@             Coverage Diff             @@
##           develop     #462      +/-   ##
===========================================
- Coverage    48.04%   47.31%   -0.73%     
===========================================
  Files           72       72              
  Lines        11242    11450     +208     
===========================================
+ Hits          5401     5418      +17     
- Misses        5841     6032     +191     

[GPMueller]

I updated this PR to the current develop version. @SpiritSuperUser could you please check whether your feature still works as intended?

Note, unit tests should still be implemented in order to avoid accidentally breaking it and providing a broken feature.