Windows and Linux support

[sindresorhus]

PR => #4

Gonna wait until electron-packager resolves some of its issues:

• --all option electron/packager#40
• --asar should be enabled by default electron/packager#35
• --arch should default to host arch electron/packager#36
• Infer from package.json electron/packager#37

[sindresorhus]

Seems like it's possible now with little config using the the --all flag: electron/packager@a157f71

I'm busy right now, but PR welcome if you want to see this.

[martijnrondeel]

electron-packager . --out=dist --app-version=$npm_package_version --prune --asar --overwrite --all fails on my system (Windows 10) because of $npm_package_version (related issue), %npm_package_version% works however. Should there be a note somewhere about this?