Feature: specify interface using the interface "index"

[GhostofGoes]

Support for Unix and Windows interface indices as a new argument to get_mac_address. On Windows, we could use wmic, while on Unix and Python 3 we can use socket.if_indextoname().

• Investigate if it's worth adding to the API (evaluating use cases) and if it can be done in a platform-agnostic manner
• Determine level of effort for platforms
• Add issues for each relevant platform.

Platforms with a high level of effort can be deferred post-1.0. Want investigate and implement a stable API with at least one platform implementation before locking the API for the stable release.