Fetter

Improvements to path expansion.

Implemented `cache-duration` to permit creating and using a locally stored JSON scan cache for the provided duration.

Implemented `bound-options` to permit selecting optional dependencies in pyproject.toml files.

Implemented home-path display abbreviation with `~`.

Handle combining multiple `DepSpec` in producing `DepManifest`.

Added `--pattern` and `--case` options to `audit`.

Added support for creating `DepManifest` from `pyproject.toml`.

Permit `DepManifest` to be retrieved from a URL.

Corrected Cargo.toml keywords.

All subcommands now have their output sub-subcommands set to `display` by default.

The `validate` and `audit` subcommands now return a non-zero exit code when items are found.

The CLI now exits for unsupported platforms.

Extended `validate` and `audit` commands to return a non-zero error code if `display` prints records.