use cross platform HOME

[springmeyer]

process.env.HOME does not exist on windows, but process.env.HOMEPATH does. process.env.HOME is used many places, even by dependencies of TileMill, so we should likely do at startup in index.js on windows:

if (process.platform == 'win32') {
    process.env.HOME = process.env.HOMEPATH;
}

Unless there is reason to store documents in a custom location. Needs more research.