JSON: Are we removing string paths?

@dgreisen this normalizePath function breaks string based paths:
https://github.com/share/ShareJS/blob/master/lib/types/json-api.js#L58

Are we intentionally deprecating context.get('foo') and requiring people to write context.get(['foo'])? If so this should throw an error. Otherwise we can delete normalizePath, Array#concat automatically wraps things in an array when necessary.

Currently this creates a bug, appending undefined to the path array.