EBP creation

[alextarasov1]

Added support for creating EBPs. Receiver types for EBPs changed to pointers in order to allow for modification. Data function added to convert EBPs back into raw bytes. Added GroupingFlag into EncoderBoundaryPoint interface since it is a common flag between Comcast and Cablelabs EBPs.

Example of new functionality:

e := ebp.CreateCableLabsEbp()
e.SetFragmentFlag(true)
e.SetConcealmentFlag(true)
e.SetExtensionFlag(true)
e.SetPartitionFlag(true)
e.SetSapFlag(true)
e.SapType = 0x02
e.SetGroupingFlag(true)
e.Grouping = []byte{0xFF, 0x7F}
e.SetTimeFlag(true)
e.SetEBPTime(time.Unix(0, 1396964696553818999).UTC())
e.PartitionFlags = 0x03
e.ReservedBytes = []byte{0x04, 0x05}
fmt.Printf("%X\n", e.Data())

[WillGunther]

Phew, finally a shorter one! This generally looks good. There is a lot of code duplication that I'm thinking might be avoided through go type embedding

[mikereedell]

Can these type and interface definitions be moved to ebp.go? We want to move away from using doc.go like this as it should only be used for documentation.

[WillGunther]

Looks good, thanks for addressing the docs changes.

Changes have been addressed