namespace prefix is mandatory for ATTR

See #210, release log:

• ee59c83 by @yegor256: #210 prefix for ns
• ba5f732 by @yegor256: doc
• 7dbaf7e by @yegor256: Merge pull request #208 from y...
• 4e8a8e3 by @yegor256: ping
• 954187d by @yegor256: new version in README
• f9aed86 by @yegor256: on push

Released by Rultor 2.0-SNAPSHOT, see build log