[pinpoint-apm#2708] 1.6.1-RC1 release

(1.6.1-SNAPSHOT -> 1.6.1-RC1)
(cherry picked from commit fee31af)

Add a note on 1.6.0

Merge pull request pinpoint-apm#1671 from koo-taejin/pinpoint-apm#1668

1.5.2 release pinpoint-apm#1668

1.5.1 release

1.5.0 tagging

1.1.2 tagging

Merge pull request pinpoint-apm#941 from koo-taejin/1.1.x

1.1.1 release pinpoint-apm#937

Merge pull request pinpoint-apm#693 from koo-taejin/pinpoint-apm#692

1.1.0 release pinpoint-apm#692