CHANGELOG: Standardize format (#611)
CHANGELOG: Standardize format (#611)

This switches the CHANGELOG to the format defined at
http://keepachangelog.com/en/1.0.0/.

See also uber-go/dig#180. Unlike the Dig PR, only v1.0 onwards were
updated with Added/Removed/etc. information.
uber-go/fx,uber-go/fx