Discontinuity parsing test
Add an example m3u8 with discontinuities and the correct parsed JSON.
Clear buffered segments on seek
If we're approaching a discontinuity, there may be segments queued up waiting to be appended. Make sure those are cleared if we seek. Add tests.
Update the currentTime when crossing a discontinuity
We have to call abort() before crossing a discontinuity, which resets the currentTime to zero. Reset the current time to the appropriate value for the segment after appending.