Add constructor parameter, `extend`, to extend and return the coerced object

[bruth]

Derived from #1. The Synapse constructor can take a boolean designating whether to wrap the passed in object with the public API methods observe, notify, and sync, i.e. Synapse(object, [extend]):

var elem = Synapse('input', true), // returns the matched object for the hook (e.g. jQuery object)
    data = Synapse({}, true);

data.observe(elem);

elem instanceof jQuery; // true

[bruth]

Slight change.. using Synapse as a function (rather than a constructor with new) augments the object that is passed in with observe, notify, and sync.