Make python-magic an optional dependency?

[satya-waylit]

Looks like #82 removed a hard dependency on python-magic. Would it be appropriate to make it an optional dependency? This would allow installation on Windows. I'm happy to make a PR if so.

[mindflayer]

Hi @satya-waylit, I spent some time investigating alternatives and I found out there is a pure-Python implementation of magic. From now on Mocket will rely on it.

[mindflayer]

Here it is: https://pypi.org/project/mocket/3.13.1/