In the array and number cases, this meant removing 'Value' from the method
name.

In the number case, this meant removing 'get' from the method name to
match the interface of java.lang.Number.

Although these two changes seem inconsistent at first glance, they work
well together from a using-the-api perspective, because chained expressions
now look like

    get("foo", JsonNumber.class).floatValue();

rather than:

    getValue("foo", JsonNumber.class).getFloatValue();

which is unnecessarily repetitive.
Improved convenience implementations of getString() and getInt()
Replaced get(..., Class) methods with getNumber, getObject, getArray.

This change is intended to make JsonObject and JsonArray more pleasant to program against.