Generalize Douglas Rachford's internal reflection

[kellertuer]

From a discussion today this PR generalises the R keyword and the reflect operation of DouglasRachford in two senses

• reflect now uses the default retraction and default inverse retraction (with keywords) instead of exp and log
• R passes retraction_method and inverse_retraction_method (new keywords of DR) to the reflection it calls
• reflection_evaluation can now be set to InplaceEvaluation in case R works in place.

[codecov[bot]]

Codecov Report

Merging #296 (55b2523) into master (3c8d3e1) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #296   +/-   ##
=======================================
  Coverage   99.74%   99.74%           
=======================================
  Files          77       77           
  Lines        7072     7084   +12     
=======================================
+ Hits         7054     7066   +12     
  Misses         18       18           

Files	Coverage Δ
src/functions/manifold_functions.jl	100.00% <100.00%> (ø)
src/solvers/DouglasRachford.jl	100.00% <100.00%> (ø)

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