Documentation build on Windows

[carlescufi]

Currently building the documentation requires make. As a documentation developer I would like to be able to build the doc on Windows-based machines. The things that need to happen in order for this to work:

• Convert Makefile to CMake
• Convert doc/Makefile to CMake
• Check that the sphinx and breathe, alongside genrest, work correctly on Windows

[carlescufi]

cc @ru-fu

[nashif]

sphinx already generates a bat script for windows, IMO we should use that instead of creating out own using cmake

[carlescufi]

@nashif but then we would have to have specific instructions per platform, and on top of that we need to run things like genrest.py. This allows us to have a single codebase to build on all platforms, and one that is consistent with our build system.