Fixed typos.
Inside of the PackageManager, change type of m_packages from Package[][string] to Package[], as there is no need for an associative array, currently.
Automatic discovery of sub-packages added to package manager.
With discoverable subpackages, the examples are named like their folder.
When it is allowed to name these differently, the package id would be rather strange for the normal usecase (e.g. a dependency on dub/examples/app/app would be required)
When a package having externally defined subpackages is installed, they work. Currently not tested with the registry.
Revert "With discoverable subpackages, the examples are named like their folder."

This reverts commit 440089bc8e0da76a24710b9ce4dc80378b62c883.

Automatic discovery is disabled.