Use unordered_map rather than map
Use unordered_map rather than map

    `unordered_map` containers are faster than map containers to
    access individual elements by their key, although they are
    generally less efficient for range iteration through a subset
    of their elements.

    http://www.cplusplus.com/reference/unordered_map/unordered_map/

Which is fine, because we never do range iteration on these maps,
so use the tiny bit faster one.

puppetlabs/mc0d,puppetlabs/mc0d