Add power of 2 for all quadtrees

[tzaeschke]

Use the power-of-2 approach (Issue #42 and PR #43) for all quadtree type indexes.
This approach immensely reduces precision errors.

[codecov]

Codecov Report

Attention: Patch coverage is 23.45679% with 62 lines in your changes missing coverage. Please review.

Project coverage is 74.73%. Comparing base (fc9e7fd) to head (d6c239d).
Report is 3 commits behind head on master.

Files	Patch %	Lines
...in/java/org/tinspin/index/qtplain/QuadTreeKD0.java	40.90%	10 Missing and 3 partials ⚠️
...java/org/tinspin/index/qthypercube/QuadTreeKD.java	40.00%	8 Missing and 1 partial ⚠️
...ava/org/tinspin/index/qthypercube/QuadTreeRKD.java	25.00%	9 Missing ⚠️
...n/java/org/tinspin/index/qtplain/QuadTreeRKD0.java	0.00%	9 Missing ⚠️
...va/org/tinspin/index/qthypercube2/QuadTreeKD2.java	11.11%	8 Missing ⚠️
...rc/main/java/org/tinspin/index/util/MathTools.java	0.00%	4 Missing ⚠️
src/main/java/org/tinspin/index/PointMap.java	0.00%	3 Missing ⚠️
src/main/java/org/tinspin/index/PointMultimap.java	0.00%	3 Missing ⚠️
src/main/java/org/tinspin/index/BoxMap.java	0.00%	2 Missing ⚠️
src/main/java/org/tinspin/index/BoxMultimap.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #44      +/-   ##
============================================
- Coverage     74.77%   74.73%   -0.05%     
- Complexity     2084     2118      +34     
============================================
  Files            76       77       +1     
  Lines          8061     8156      +95     
  Branches       1576     1593      +17     
============================================
+ Hits           6028     6095      +67     
- Misses         1644     1660      +16     
- Partials        389      401      +12     

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