Mark a task which can not be performed, without deleting it

See #46, release log:

• 038fa7a by @yegor256: #46 restrict
• 7398a56 by @yegor256: #46 proc
• faff815 by @yegor256: #46 postpone()
• 785d96f by @yegor256: #50 minitest reporters
• e9fc85a by @yegor256: #50 thin

Released by Rultor 1.68.5, see build log