Version 0.3.0

Features

• Package definitions now have a detailed variant available, mimicking the
  Cargo.toml format. This has been implemented in order to enable one to
  specify which features should be compiled in the installed packages, by
  configuring a list of feature flags in a similar format to the Cargo
  manifest's [features] section. Many thanks to @MaeIsBad: #2.
• A new --only-self option has been added to the ship command: it enables
  one to only update cargo-liner and nothing else. It is incompatible with
  --no-self.
• Short variants of the options flags of the ship command are now enabled.
• A new --keep-self option has been added to the import command: it
  ensures the cargo-liner package is kept in the package list and thus
  written to the created configuration file. It is compatible with the version
  operator selection options.
• Basic logging has been implemented. Messages will therefore now be displayed
  in order to inform the user about the currently performed action and its
  results. Errors bubbling up are manually caught in the global main function
  and logged using the same format as the rest of the emitted messages.
• New --verbose and --quiet option flags have been implemented. They
  control the global verbosity of the program by changing the logging
  configuration at runtime. They are both available globally, i.e. with or
  without a command and before or after the command name. They can both be
  repeated up to three times in order to adjust how much the verbosity is
  changed. They are incompatible with each other. It is made sure they arrive
  last in the CLI help messages, but still just before --help and
  --version.

Fixes

• The --no-self-update option of the ship command has been renamed to
  --no-self. This makes it more consistent with other new option flags.
• The TOCTOU bug for the configuration file import has been fixed: between
  checking for the existence of the file and then possibly overwriting it, a
  new file could appear. The --force option flag now controls which
  operation is used: when present, the previously always used overwriting is
  called; when absent, an appropriate system call is made to ensure only
  creating a new file is possible atomically.
• Fixed some Clippy warnings triggered on the test suite.

Documentation

• README.md:
  • Fixed the CI status badge.
  • Added missing shell syntax highlighting for the code block showing the
    output example.
  • Clarified CLI option defaults.
  • Updated outputs.
  • Various other small adjustments.
• New features.

Testing

• The GitHub CI workflow now denies rustdoc warnings by default. Thanks
  to @MaeIsBad: #3.
• Appropriate tests have been added alongside the new functionalities.