exclude max and min from sigma calculation

See #80, release log:

• 2a8d121 by @yegor256: #80 format
• 0a48c3c by @yegor256: #80 layout
• 6e301a7 by @yegor256: #80 exclude min and max
• 57c6d90 by @yegor256: #80 show min and max
• b3bae35 by @yegor256: #80 range
• 7450c8a by @yegor256: #80 cactus 0.25.4

Released by Rultor 1.66.3, see build log