update doc for releasing

[maven-release-plugin] copy for tag antlr4-master-4.8-1

[maven-release-plugin] copy for tag 4.7.2

[maven-release-plugin] copy for tag 4.7.1

[maven-release-plugin] copy for tag 4.7

[maven-release-plugin] copy for tag 4.6

heading towards 4.6

Update releasing-antlr.md

[maven-release-plugin] copy for tag antlr4-master-4.5.3