Parse Low-Latency HLS playlists

[robwalch]

This PR will...

Adds support for Low-latency HLS playlist parsing https://tools.ietf.org/html/draft-pantos-hls-rfc8216bis-07#section-4.4.3.8

• EXT-X-SERVER-CONTROL attributes are added to level details
  • levelDetails.canBlockReload: boolean
  • levelDetails.canSkipUntil: number
  • levelDetails.canSkipDateRanges: boolean
  • levelDetails.partHoldBack: number
  • levelDetails.holdBack: number
• EXT-X-PART-INF: PART-TARGET attribute is added to level details
  • levelDetails.partTarget: number
• EXT-X-PART tags are added to fragments (parts for incomplete fragments will be added to the fragment list later when loader support is added)
  • levelDetails.fragments[].partList: { duration: number, gap: boolean, independent: boolean, uri: string }
• EXT-X-GAP is added to fragment.tagList
• EXT-X-BITRATE is added to fragment.tagList
• EXT-X-PRELOAD-HINT attributes are added to level details
• EXT-X-RENDITION-REPORT list is added to level details

Why is this Pull Request needed?

This work is a precursor to adding support for delta playlist updates, playlist block reloading, part support, and cdn tune-in.

Are there any notes?

In order to implement HOLD-BACK start time for live, the config passed in is no longer mutated. It is added to the merged config as userConfig so that we can distinguish between default options and options set by the user. This allows us to use hold-back as the target latency when the user has not set liveDurationSync/liveDurationSyncConut.

Checklist

• changes have been done against master feature/v1.0.0 > apple-ll-hls branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md