add Image2 and Muxers options. require Elixir 1.12

allow FFprobe on remote URLs

use Rambo instead of erlexec, require Elixir 1.9

fix running erlexec as root

fix SHELL env check

to_stdout/1, execute/1 returns {:ok, output}

relax jason dep ~> 1.2

jason 1.2

fix -loop in FFmpex.Options.Advanced

FFprobe API changes for better error handling