Emscripten: Override NO_FILESYSTEM=1

[dasa]

I'm getting this warning in my build: warning: unresolved symbol: $FS

This goes away if I comment out this line:
https://github.com/charto/nbind/blob/master/src/nbind.gypi#L35

Is there a better way to remove this or maybe it should be removed from src/nbind.gypi since it seems that Emscripten should remove it when needed:
http://kripken.github.io/emscripten-site/docs/optimizing/Optimizing-Code.html?highlight=no_filesystem#miscellaneous-code-size-tips

[jjrv]

I'll try to release version 0.4.0 soon, where the .gypi file will be stored inside your project instead of under node_modules/nbind. This should make it easier to customize the options.