Xcode project origin

This commits introduces protagonist.node development with Xcode with
following limitations:

1. Node v0.10.33 has to be installed, see `Header Search Paths` in the
`protagonist` target settings
2. sundown.a markdownparser.a snowcrash.a has to be already built (use
`node-gyp rebuild` or `npm install`)
3. the product still needs to be tested from CLI using `make test`