Traps missing login/password settings early

This commit checks that the PUBLISHER_LOGIN and PUBLISHER_PASSWORD
environment variables has been set and if not, reports it as an
error and exits.
Bumps version to 1.0.0-rc1 and uses forge-maven-plugin 3.0.3-rc1
Merge pull request #1 from cloudsmith/master

Improved error reporting and dependency checks off by default