notify users on new puzzles

See #31, release log:

• 1e32665 by @yegor256: #31 rultor config
• bc408f8 by @yegor256: #31 ping
• 106e661 by @yegor256: #31 typo
• 31b5e5a by @yegor256: #31 cc
• af0b1b6 by @yegor256: #31 sources
• ef9fd68 by @yegor256: #31 puzzle removed
• ee142b0 by @yegor256: #31 new puzzle
• 053412c by @yegor256: #31 ping
• 9d6974d by @yegor256: #31 file basename
• 0197821 by @yegor256: #31 log removed
• 8b12e48 by @yegor256: #31 extra log
• 0f67144 by @yegor256: #31 new puzzle
• b2c602f by @yegor256: #31 log config
• cd11758 by @yegor256: #31 puzzle removed
• 4eb9ef0 by @yegor256: #31 test_github_tickets
• 9e6ce96 by @yegor256: #31 test puzzle
• c24b0b2 by @yegor256: #31 more tests
• 2b7ade9 by @yegor256: #31 more logs
• 87f7b95 by @yegor256: #31 puzzle off
• 783d813 by @yegor256: #31 typo
• and 12 more...

Released by Rultor 1.62.2, see build log