GitLab

* update documentation dependencies

add version number to docs

rename doc config directories

enable more doc formats on rtd

add license section in docs

* Add contraction profiler and tests

* Build and style fixes

* Allow to use any elementwise operator for ref_contraction

* Introduce profile_contraction_scale and profile_contraction_bilinear

* Make ref_contraction generic and extend interface tests

* Stylistic minor fixes

* Extend test_contraction_interface