SumOf... to accept numbers

See #459, release log:

• f806833 by @yegor256: #459 NumberOf
• e263590 by @yegor256: #459 new method
• d324b97 by @yegor256: #449 more javadoc
• 5e691b1 by @yegor256: Merge branch 'master' of githu...
• fabd728 by @yegor256: #459 SumOf
• e9668e5 by @rultor: Merge branch '__rultor'
• ee57962 by @yegor256: Merge pull request #431 from g...
• 5305135 by @yegor256: javadoc.io new badge

Released by Rultor 1.66.3, see build log