Add new methods of underscore.js v1.6

[serkanyersen]

Implement new methods with their respective tests

• Added _.partition, a way to split a collection into two lists of results — those that pass and those that fail a particular predicate.
• Added _.property, for easy creation of iterators that pull specific properties from objects. Useful in conjunction with other Underscore collection functions.
• Added _.matches, a function that will give you a predicate that can be used to tell if a given object matches a list of specified key/value properties.
• Added _.constant, as a higher-order _.identity.
• Added _.now, an optimized way to get a timestamp — used internally to speed up debounce and throttle.
• The _.partial function may now be used to partially apply any of its arguments, by passing _ wherever you'd like a placeholder variable, to be filled-in later.
• The _.each function now returns the original iterated list (just like it used to), for better chaining.

Make sure API matches the javascript API.

[serkanyersen]

Functionality boosted to 1.6