Merge branch 'release/2.1.5' into develop
Merge branch 'develop' of github.com:pearson-enabling-technologies/elasticsearch-approx-plugin into develop
Enabled post mode
comments for  filed data type and mode changes
updated changelog & documentation for v2.1.6
version 2.1.6
'post'/'collector' mode fixes
change tests to reflect post/collector modes
Merge branch 'release/release'