knn classification

[s-weil]

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Closes 300

Please list the changes introduced in this PR

• added first version for the KNN classification

Description

The KNN algorithm is implemented in different versions [see ML\Unsupervised\KNN.fs], namely

• for arrays
• sequences
• via a classification object (with convencience methods) Code documentation, examples and unit tests are provided.

NOTE: further specialisations of the algorithm for improved performance exist and versions are possible (such as a vector version). Moreover one could consider the feature of parallelized predictions (may only make sense in case of a big point cloud).

• [x] The project builds without problems on your machine
• [x] Added unit tests regarding the added features

[codecov-commenter]

Codecov Report

Attention: 32 lines in your changes are missing coverage. Please review.

Comparison is base (4719e96) 47.00% compared to head (8f887a5) 47.16%. Report is 2 commits behind head on developer.

Files	Patch %	Lines
src/FSharp.Stats/ML/Unsupervised/KNN.fs	28.20%	25 Missing and 3 partials :warning:
tests/FSharp.Stats.Tests/ML.fs	94.28%	0 Missing and 4 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## developer #310 +/- ## ============================================= + Coverage 47.00% 47.16% +0.15% ============================================= Files 148 149 +1 Lines 16458 16567 +109 Branches 2219 2230 +11 ============================================= + Hits 7736 7813 +77 - Misses 8052 8077 +25 - Partials 670 677 +7 ```

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[bvenn]

Thanks for this awsome and well prepared addition @s-weil!