Add nx.Event spec
Add chai-spies plugin reference
Add onvalue spec for nx.Property
Add chai-spies to .gitignore
Remove unbind() from nx.Property specs
Remove 'nx.Binding as a parameter' test
Add non-unique handler name exception spec stub for nx.Event
Add 'trigger-all' test for nx.Event
Make nx.Event specs use chai-spies
Remove sync() from nx.Binding
Add draft bindings implementation