Replace WriteString with WriteRune
Replace WriteString with WriteRune

Before:
BenchmarkDecodeMasterPlaylist-4   100000             22461 ns/op           12194 B/op         77 allocs/op
BenchmarkDecodeMediaPlaylist-4       100          16692449 ns/op        10999880 B/op     120059 allocs/op
BenchmarkEncodeMasterPlaylist-4  1000000              1025 ns/op              40 B/op         11 allocs/op
BenchmarkEncodeMediaPlaylist-4       100          13014814 ns/op         1736192 B/op      81207 allocs/op

After:
BenchmarkDecodeMasterPlaylist-4   100000             22482 ns/op           12194 B/op         77 allocs/op
BenchmarkDecodeMediaPlaylist-4       100          15918199 ns/op        10999881 B/op     120060 allocs/op
BenchmarkEncodeMasterPlaylist-4  1000000              1058 ns/op              40 B/op         11 allocs/op
BenchmarkEncodeMediaPlaylist-4       100          12738933 ns/op         1736192 B/op      81207 allocs/op

bcasinclair/m3u8,grafov/m3u8