Windows support for magic

[epicfaace]

In Windows, magic must be initialized with the kwarg magic_file that gives the path of the .magic file. This PR:

• Allows for Windows support by allowing the .magic file to be specified by the MAGIC_FILE_PATH setting in settings.py.
• Further documentation in the README to describe how to set this up on Windows.

(Similar PR on original repository here: kaleidos#13)

[mbourqui]

Thank you for your interest in this project (the original one and my fork)!
Since my fork differs in structure from the original repo, your PR conflicted with this repo. I had to manually replicate your changes, but it's all merged.
I also pushed a new release on PyPi, so you can benefit from your changes as of now :)

[epicfaace]

Thanks!