To avoid reimplementing the device selection logic in extensions, we
introduce a new environment variable NITROCLI_RESOLVED_USB_PATH that is
set to the USB path of the single matching Nitrokey device. If no device
matches, or if there are multiple matching devices, the variable
is not set.

With upcoming changes we will have not only the main crate (comprised of
two binaries), but an entire workspace containing extensions and other
support crates.
This change instructs the CI to build and test these crates as it does
for the main crate.

This patch adds the extension support crate nitrocli-ext as a workspace
member. This crate contains useful methods for extensions written in
Rust, providing access to the nitrocli binary and to the nitrokey-rs
library.

This patch adds the nitrocli-otp-cache extension that caches OTP data.
The per-device cache stores the names, OTP algorithms and IDs of the
slots It can be used to access the slots by name instead of slot index.

Fix compiler warnings for dynamic assert messages seen with rustc 1.51.

Some of our tests compare byte slices and are very hard to debug if the
assertion fails due to they way these slices are printed. This patch
adds assertion messages containing the (lossy) string representation of
the byte slice to make it easier to debug errors.

Fixes d-e-s-o#152

The format specifier we use for printing errors returned by the main
program will include a backtrace in the output -- if one is available.
That's not necessarily a feature that we need: the causal chain of
errors should be sufficient and end users are unlikely to have use for a
backtrace.
This change adjusts the format specifier so that we only print the chain
of errors, albeit in a slightly different format:
- Previously:
  > Failed to generate OTP
  >
  > Caused by:
  >     Command error: The given slot is not programmed

- New:
  > Failed to generate OTP: Command error: The given slot is not programmed

This patch adds a configuration for GitHub Actions that builds and tests
nitrocli with the MSRV, stable, beta and nightly Rust, calls clippy and
rustfmt and checks the license annotations with reuse-tool.

With the addition of the GitHub Actions workflow we have found a better
working replacement for the GitLab CI. To that end, we no longer want to
use the latter.
This change removes the corresponding configuration from the repository.

This patch adds an --only-aes-key option to the reset command to only
build a new AES key without performing a full factory reset.

Fixes d-e-s-o#69

This patch adds the pws-cache core extension that allows accessing the
PWS slots by their name instead of the slot index.

Fixes d-e-s-o#155.