update changelog and bump version

1.6.4

version 1.6.3

bump version to 1.6.2

Bump version for new error-comparison feature

Version 1.6.0

Version 1.5.0

Bump to 1.4.0

Incrementing minor version since MismatchException base class changes.

Update changelog and version for 1.3.0 release

Version 1.2.0

- New: Use monotonic clock for duration calculations
- New: Drop support for ruby <2.1 to support monotonic clock
- New: Run CI on Ruby 2.5