docs: update contributing
refactor: hide private functions
refactor: don't use glob import for `chrono`

Just for readability.
docs: update contributions steps
docs: it's i3status-rust

Not i3status-rs.
docs: don't show `help` in demo

The `--help` contains the app version.
While the API stays the same, the version number makes users think
the repo was not updated correctly.
docs: update release script path
docs: master branch is not protected

We host zman on sr.ht, so the master branch is not protected
refactor: duplicate code
style: change app icon
test: add more unit tests
refactor: rename function name for readability

rename `get` to `compute`
fix: wrong month and week ratio computation
docs: improve docs
docs: zman now support time char prefix and icon
docs: i3status.rs example configs
fix: i3status.rs can't accept unicode icon
Revert "feat: ability to set app icon"

This reverts commit 890c0fa3bcdf0e4e80f68b79a59f0ce53e107907.
test: add unit tests