Use open3 for shell command execution

[tomekr]

It looks like the the run method takes the filename input and interpolates it into a backtick shell command without validating the filename. This can result in a code execution vulnerability should users of this wrapper not validate the filename (which could come from an untrusted source).

See this article for more information (https://www.hilman.io/blog/2016/01/stop-using-backtick-to-run-shell-command-in-ruby/)

This PR uses the Open3 standard library to execute the command which will make sure that the parameters to the soxiare properly escaped. It also adds some error handling should the soxi binary return an error.

[clauswitt]

Thanks for your pr. I have decided not to merge this, but to make a minor rewrite to the gem instead. (I have credited you in both the readme and the commit (3a52d77) message though).

As the readme says (now) we have abandoned this gem (we no longer use it). But I decided to make a release based on your suggestions (however adding some error raising instead of just printing a string)