Object APPEND, COPY, LENGTH?

In addition to standard object actions, R3 allows:

	append	extends the object with new word/value pairs (the input object is modified). New words must not already be fields of the object, or an error will result. Words can be word or set-word values. No binding is done on the data value parts (so words within blocks and functions do not get bound to the new context).
	copy	clone the object. Deep copy all series within it. Currently, no rebinding is done. (Words within blocks and functions do not get bound to the new context.)
	length?	return the number of instance variables. (Faster and less garbage than doing a `length?` `first` operation.)

Example of append:

>> a: make object! [b: 10]
>> append a [c: 20]
== make object! [
        b: 10
        c: 20
   ]

To get the length:

>> length? a
== 2

The copy function works as you would expect.

Why not insert, remove, etc.?

Why not allow insert and other series modifying functions to work on objects? Because they would corrupt the bindings of words within the object.

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