Support EXT-X-SCTE when encoding playlists

[bradleyfalzon]

Expands upon #40 to support encoding the SCTE segments into a playlist.

Such that the following:

package main

import (
        "fmt"

        "github.com/grafov/m3u8"
)

func main() {
        p, _ := m3u8.NewMediaPlaylist(1, 1)
        _ = p.Append("test01.ts", 5.0, "")
        _ = p.SetSCTE("CueData", "ID", 3.141)
        fmt.Print(p.String())
}

Outputs:

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-TARGETDURATION:5
#EXT-X-SCTE:CUE="CueData",ID="ID",TIME=3.141
#EXTINF:5.000,
test01.ts

[bradleyfalzon]

@vishal24tuniki if you have a moment, can you look over this and ensure it's behaving as expected, if you're OK with it, I'll merge.

[vishal24tuniki]

@bradleyfalzon Yes sure, will go over it in couple of hours :)

[vishal24tuniki]

Correct the tag to #EXT-SCTE35 from #EXT-X-SCTE

[vishal24tuniki]

@bradleyfalzon Everything looks fine. Just the SCTE tag is wrong as mentioned in the inline code comments

[bradleyfalzon]

Brilliant, thanks @vishal24tuniki

[vishal24tuniki]

#EXT-SCTE: is still wrong, its #EXT-SCTE35: