pmd: update release process documentation

  pmd.website.baseurl is set correctly if the profile "pmd-release" is used
  during releasing
pmd: format source, no changes
pmd: fix #1171 Specifying minimum priority from command line gives NPE
pmd: fix #1175 false positive for StringBuilder.append called 2 consecutive times
pmd: verify #1173 Java 8 support: method references
pmd: fix #1170 false positive with switch in loop