Support for working with Package Configuration files as described in the Package Configuration v2 design document.

The primary libraries are

• package_config.dart: Defines the PackageConfig class and other types needed to use package configurations, and provides functions to find, read and write package configuration files.

• package_config_types.dart: Just the PackageConfig class and other types needed to use package configurations. This library does not depend on dart:io.

The package includes deprecated backwards compatible functionality to work with the .packages file. This functionality will not be maintained, and will be removed in a future version of this package.