Issue #40 fixes

[tzaeschke]

The test provided in issue #40 (for a possible ArrayOutOfBoundsException) revealed a number of problems related to removing and inserting entries. This PR is a cumulative fix for these.

[codecov]

Codecov Report

Attention: Patch coverage is 59.18367% with 20 lines in your changes missing coverage. Please review.

Project coverage is 75.10%. Comparing base (fc9e7fd) to head (fb7761e).

❗ Current head fb7761e differs from pull request most recent head 46bd1c7

Please upload reports for the commit 46bd1c7 to get more accurate results.

Files	Patch %	Lines
...ain/java/org/tinspin/index/qthypercube2/QNode.java	57.44%	17 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #41      +/-   ##
============================================
+ Coverage     74.77%   75.10%   +0.32%     
- Complexity     2084     2113      +29     
============================================
  Files            76       76              
  Lines          8061     8090      +29     
  Branches       1576     1581       +5     
============================================
+ Hits           6028     6076      +48     
+ Misses         1644     1617      -27     
- Partials        389      397       +8     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.