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[bot]]

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 :warning:
...java/org/tinspin/index/qthypercube/QuadTreeKD.java	40.00%	8 Missing and 1 partial :warning:
...ava/org/tinspin/index/qthypercube/QuadTreeRKD.java	25.00%	9 Missing :warning:
...n/java/org/tinspin/index/qtplain/QuadTreeRKD0.java	0.00%	9 Missing :warning:
...va/org/tinspin/index/qthypercube2/QuadTreeKD2.java	11.11%	8 Missing :warning:
...rc/main/java/org/tinspin/index/util/MathTools.java	0.00%	4 Missing :warning:
src/main/java/org/tinspin/index/PointMap.java	0.00%	3 Missing :warning:
src/main/java/org/tinspin/index/PointMultimap.java	0.00%	3 Missing :warning:
src/main/java/org/tinspin/index/BoxMap.java	0.00%	2 Missing :warning:
src/main/java/org/tinspin/index/BoxMultimap.java	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ 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 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.