Alternative API to add arguments sequentially, instead of Builder pattern

[talklittle]

The current API is a Builder, where files are added to the Command builder, and then Streams and Options are added to each file. This is the reverse of the ffmpeg command-line API, where options are specified before the corresponding file.

Current way:

command =
  FFmpex.new_command
  |> add_global_option(option_y())
  |> add_input_file("input.avi")
  |> add_output_file("output.avi")
    |> add_stream_specifier(stream_type: :video)
      |> add_stream_option(option_b("64k"))
    |> add_file_option(option_bufsize("64k"))

Corresponds to:

$ ffmpeg -y -i input.avi -b:v 64k -bufsize 64k output.avi

---

New alternative:

In some situations a more direct mapping of the command-line API to Elixir may be desirable instead of the Builder. It would essentially be a wrapper around Elixir's System.cmd/3 (or Rambo.run/3) with some convenience functions.

Maybe FFmpex.new_raw_command/0 and a RawCommand struct and add_raw_argument/2?

raw_command =
  FFmpex.new_raw_command
  |> add_raw_argument("-y")
  |> add_raw_argument(["-i", "input.avi"])
  |> add_raw_argument(["-b:v", "64k"])
  |> add_raw_argument(["-bufsize", "64k"])
  |> add_raw_argument("output.avi")

Related: #28