Introduce a `RetractionWithKeywords` to specify / fix keywords on Layer 1

[kellertuer]

This is a continuation of https://github.com/JuliaManifolds/Manifolds.jl/issues/547, to introduce retractions (and inverse retractions and vector transports) where you can fix keywords in the retraction types.

This is necessary since keywords only act on layer 3 on the actual implementation – and with this step they are “added” in layer two before “resolving” the retraction type and passing them down to layer 3.

[codecov[bot]]

Codecov Report

Merging #130 (d6bddf6) into master (437f341) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #130   +/-   ##
=======================================
  Coverage   99.81%   99.82%           
=======================================
  Files          18       18           
  Lines        2200     2247   +47     
=======================================
+ Hits         2196     2243   +47     
  Misses          4        4           

Impacted Files	Coverage Δ
src/ManifoldsBase.jl	99.31% <ø> (ø)
src/parallel_transport.jl	100.00% <100.00%> (ø)
src/retractions.jl	100.00% <100.00%> (ø)
src/vector_transport.jl	100.00% <100.00%> (ø)

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[kellertuer]

The retraction case should be finished (including tests); If this is a way we want to go, the other two are not much work to do, but I would like to be sure that this is a good approach.

[mateuszbaran]

I think this new retraction looks fine, this is a good approach.

[mateuszbaran]

Sorry for closing, I've accidentally clicked the wrong button.

[kellertuer]

So this should be feature complete, but I have to take a look how to test the final variant, the VectorTransportWithKeywords.

[kellertuer]

I checked the missing lines - the one case (mid point on <=1.1) is called so that is a false positive; where I am not sure whether maybe the 1.1 just did not report properly.

The other – on ValidationManifolds, I checked and hopefully fixed.