Split the esp8266 core out into a core repository that can be downloaded into the Arduino/hardware folder in documents

[ricklon]

Split the esp8266 core out into a core repository that can be downloaded into the Arduino/hardware folder in documents.

This allows for the development of the core not to be tied directly to the IDE.

I've created a core based on this here:
https://github.com/ricklon/esp8266-core

The only major issue is that the tools folder should be inside esp8266com

[igrr]

We're already tracking this issue in #14, closing as duplicate.