Topic/sorting 721

[ghostroad]

This is intended to resolve Issue #721, which relates to inconsistencies across the implementations of MergeSort, InsertionSort, and QuickSort.

1. All these strategies operate in place on segments of arrays that start and end at specified indices. In the QuickSort implementation, the end index was inclusive, while it was exclusive in MergeSort and InsertionSort. This has been fixed in this changeset to make the end index exclusive in all three implementations, following the convention in the Java Collections library. Validity and boundary checks have been introduced for the various parameters. Unit tests have been written to document and test the new behavior.

2. The naming of the start and end indices has been made consistent.

3. Unit tests have been added for checking correctness, stability, edge cases, etc.

4. Scaladocs have been added for all the utility methods in the Sorting package.

[codecov-io]

Codecov Report

Merging #738 into master will increase coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #738      +/-   ##
=========================================
+ Coverage   51.28%   51.4%   +0.11%     
=========================================
  Files         196     196              
  Lines       11765   11774       +9     
  Branches     1615    1591      -24     
=========================================
+ Hits         6034    6052      +18     
+ Misses       5731    5722       -9

Impacted Files	Coverage Δ
core/src/main/scala/spire/math/Sorting.scala	100% <100%> (+46.42%)	⬆️
...ore/src/main/scala/spire/math/interval/Bound.scala	48.81% <0%> (-5.52%)	⬇️
...ala/spire/math/poly/BigDecimalRootRefinement.scala	82.11% <0%> (-3.32%)	⬇️
core/src/main/scala/spire/math/Natural.scala	65.75% <0%> (-1.82%)	⬇️
core/src/main/scala/spire/math/package.scala	59.1% <0%> (-0.35%)	⬇️
core/src/main/scala/spire/math/Algebraic.scala	65.85% <0%> (ø)	⬆️
core/src/main/scala/spire/math/Interval.scala	67.86% <0%> (ø)	⬆️
core/src/main/scala/spire/math/Rational.scala	95.52% <0%> (+0.23%)	⬆️
extras/src/main/scala/spire/math/FixedPoint.scala	34.97% <0%> (+0.54%)	⬆️

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[denisrosset]

Beautiful PR! Thanks for the hard work; I've incorporated some of your notes in the future release notes.

Love the complete tests in particular.

[denisrosset]

Hi! If you'd like to see your real name in the CHANGES.md file, please make a PR towards it, I'd be happy to merge.