* tests: update to PHPUnit 6.0 with rector
* [cs] clean empty docs
* composer: bump to PHPUnit 6.4
* tests: use class references over strings
* cleanup
* travis: move coveralls here, decouple from package
* composer: use PSR4
* phpunit: simpler config
* travis: add ecs run
* composer: add ecs dev
* use standard vendor/bin directory for dependency bins, confuses with local bins and require gitignore handling
* ecs: add PSR2
* [cs] PSR2 spacing fixes
* [cs] PSR2 class name fix
* [cs] PHP7 fixes - return semicolon spaces, old rand functions, typehints
* [cs] fix less strict typehints
* fix typehints to make tests pass
* ecs: ignore typehint-less elements
* [cs] standardize arrays
* [cs] standardize docblock, remove unused comments
* [cs] use self where possible
* [cs] sort class elements, from public to private
* [cs] do not use yoda (found less yoda-cases, than non-yoda)
* space
* [cs] do not assign in condition
* [cs] use namespace imports if possible
* [cs] use ::class over strings
* [cs] fix defaults for arrays properties, properties and constants single spacing
* cleanup ecs comments
* [cs] use item per line in multi-items array
* missing line
* misc
* rebase
* Lineer Algebra operations
* Covariance
* PCA and KernelPCA
* Tests for PCA, Eigenvalues and Covariance
* KernelPCA update
* KernelPCA and its test
* KernelPCA and its test
* MatrixTest, KernelPCA and PCA tests
* Readme update
* Readme update
### Features
* Works only with primitive types int, float, string
* Implements set theortic operations union, intersection, complement
* Modifies set by adding, removing elements
* Implements \IteratorAggregate for use in loops
### Implementation details
Based on array functions:
* array_diff,
* array_merge,
* array_intersection,
* array_unique,
* array_values,
* sort.
### Drawbacks
* **Do not work with objects.**
* Power set and Cartesian product returning array of Set
