Provides core support for plug-ins and the plug-in registry.

## Package Specification

This package specifies the API related to running the platform itself. This includes area such as the definition and management of plug-ins and the starting, stopping and maintaining the platform itself. In addition, this API supplies various utility types such as `Path`, `IPath` and various flavours of progress monitors.

Clients writing plug-ins or accessing plug-in functionality will likely be interested in the types provided by this package.