Add function to merge an update to a media playlist
When an ENDLIST tag is not present, media playlists should be continually re-requested to check for updates. The updated versions of the playlist must be reconciled with the client's metadata to continue playback. Added a single function to manage this process for media playlists with and without media sequence information, using URIs and byterange information to match segments.
Removed parser code that defaulted the playlist type to VOD if no type was specified. The spec allows live streams to omit the playlist type if the server intends to remove segments from the playlist. None of the runtime code actually referenced playlist type so it may have been a bit premature to parse it at all.