Mpyg321

- pexpect added to setup.py install_requirements

Adds mute/unmute feature for mpg123

Support volume feature for mpg321

Bugfix:
- Sometimes, the process would crash after playing for more than 30sec (pexpect timeout). This should be fixed.

Performance:
- For mpg123, silence the frames output by default so that pexpect has less data to process

New Features:
- Volume
- Load list

- Adds support for audio devices

New features:
- Separate support for mpg123 and mpg321
- Possibility to set the path to the mpg123/321 program

Fixed:
- Events support of mpg123