Prepares version 1.8.2 for release.

preparing release 1.8.1

Prepare new release 1.8.0

preparing release 1.7.1 (amazon-ion#312)

prepare new release 1.7.0 (amazon-ion#309)

* prepare new release 1.6.2

* fix version number to be 1.7.0

Release 1.6.1 (amazon-ion#286)

Fixing staging nexus URL (amazon-ion#282)

software.amazon.ion Release 1.5.1

Release 1.5.1 (amazon-ion#262)

software.amazon.ion Release 1.5.0