v4.0.0 Alpha version 3

From the CHANGELOG:

• (build) Compiles to dist/ko.js
• (build) The dist/tko.js (that exported tko) has been deprecated/removed
• (internal) Add the ES6 LifeCycle class (see tko.lifecycle)
• (binding handlers) Add new-style ES6 Binding Handler class (see custom-bindings documentation and tko.bind/src/BindingHandler.js), descended from the LifeCycle class
• (lifecycle) Fix error with event handler type
• (provider) Add & document the Provider base class
• (subscribable) Add the once, then, when, yet, and next functions
• (parser) Fix early-out for logical (&& / ||) operators
• (binding) ko.applyBindings now returns a Promise that resolves when bindings are completed
• (attr) Support namespaced attributes with attr binding #27
• (options) Add the options.Promise, so users can use a their own or a safe Promise variant of A+/Promises (defaults to window.Promise)
• (attribute-interpolation) Fix interpolation of styles attribute (e.g. style="color: {{color}}") in the AttributeMustacheProvider, by adding attributesBindingMap parameter.