v0.2.1: Update README to match latest usage

Also re-add support for `--help` at commandline :/

v0.2.0: Follow the embedded-hal interface (#14)

This closes #12.

* Minor version bump `0.1.0` -> `0.2.0` due to API changes.
* Rewrite implementation to follow the `embedded-hal` interface.
* Rewrite the API to be more consistent and move bargraph specific
features from `ht16k33`.
    * Add `--debug` and `--trace` log levels.
    * Add `--as-is` to skip chip initialization if desired.
    * Add initial (trivial) `--show/show` support. (Issue #6)
    * Use Enums for feature values.
    * Hardcode the resolution, will need to make configurable later
    (Issue #13).
    * Make `clippy` happy.
* Added `embedded-hal` keyword for `crates.io`, since we're now
compliant :)
* Drop CI support for Rust `1.24.0`, there's been no request to support
it and it's quite old.

Initial crates.io publishing

Available in crates.io:

• https://crates.io/crates/led-bargraph/0.1.0