introduce 𝜋

See #9, release log:

• d477893 by @yegor256: #9 fmt
• bdc4b6e by @yegor256: #9 clippy fixed
• bd6ee49 by @yegor256: #9 pi
• d2019ba by @renovate[bot]: Update Rust crate env_logger t...
• d668b6e by @rultor: Merge branch '__rultor'
• 73cf116 by @rultor: Merge branch '__rultor'
• ae98e1a by @rultor: Merge branch '__rultor'
• 2d6a721 by @rultor: Merge branch '__rultor'
• 3d7155f by @renovate[bot]: Update Rust crate simple_logge...
• 2b7d9cf by @rultor: Merge branch '__rultor'
• 78dee16 by @rultor: Merge branch '__rultor'
• 2daf735 by @rultor: Merge branch '__rultor'
• fccb6cb by @rultor: Merge branch '__rultor'
• 5e06602 by @renovate[bot]: Update Rust crate regex to 1.6...
• 5439576 by @renovate[bot]: Update Rust crate strum to 0.2...
• 531c689 by @rultor: Merge branch '__rultor'
• d1d24e0 by @renovate[bot]: Update Rust crate itertools to...
• da10f3c by @renovate[bot]: Update Rust crate ctor to 0.1....
• 51cba38 by @rultor: Merge branch '__rultor'
• c850219 by @yegor256: #9 pi input arg
• and 29 more...

Released by Rultor 2.0-SNAPSHOT, see build log