Remove y60 support
Remove registerObserver

WebSocket-based GNPs should be used instead.
Use bower for runtime dependencies
Factor out http lib based on ES6 promises
Clean up code
Handle 2xx and 304 as successful responses
Refactor request header handling
Reformat code according to airbnb style guide
Spec and fix creation of unnamed, empty nodes
Relax hinting for specs
Refactor http lib
Remove Gom#create

Named nodes and attributes can already be created using update. "Unnamed"
nodes (that are assigned a UUID) shouldn't be used in practice, so I just
removed the functionality.
Spec node retrieval
Spec node update
Refactor option handling
Spec and fix node destruction
Refactor XML serialization
Use require syntax for dependencies
Add ES6 promise polyfill, remove jQuery dependency
Bump version number