Simplify RbPod::Collection#each.
Use RbPodError instead of built-in RuntimeError.
Don't accidentally add editor swap files to the index.
Provide RbPod::Collection#length so #size and #count will work. Update README accordingly.
Drop custom wrap/unwrap functions and use DATA_PTR directly. Also fixup whitespace and start on collection decorators.
Create helpers to construct unmanaged track/playlist collections.
Fixup RbPod::Database#tracks so it's parented by the master playlist.