Re-use #off in #connect and add context argument to #off

Objectives:

* Make it easy to extend oo.EventEmitter by only overriding #on and #off
* Add context functionality to off method
* Skip duplicate bindings

Changes:

src/EventEmitter.js
* Add duplicate skipping in on method
* Add optional context argument to off method, which defaults to null, just as it
  does within on method
* Reuse off method for actual removal of bindings inside connect method
readme: Add branch=master filter to Travis CI branch

Previously it showed the last build result in general for any
branch in the repository.
Add oo.Registry and oo.Factory

oo.Registry
* Class for registering data by one or more symbolic names

oo.Factory
* Class for registering constructors by one or more symbolic names and
  creating objects
Fix oo.Factory create and tests
Add notes for v1.0.3
Tag v1.0.3
Add getHash to core

getHash uses JSON.stringify with a callback to make ordering predictable.
It can be used to produce stable hashes of JavaScript objects.
history: Add notes for v1.0.4
Tag v1.0.4