DO NOT MERGE: spike on Javascript SDK

See examples/node-rest.js for an example how I would like the client API to look in all supported languages.

This pull requests serves as a place to discuss the proposed implementation. Note the code has a prototype quality (there's no need to point out minor coding style issues and/or bugs).

/to: @ritch @raymondfeng please review.
/cc: @altsang @Schoonology