Feature: The iki_read program should support a more generalized substitution process...

Feature: The iki_read program should support a more generalized substitution process called "replace".

In the distant past I mixed up having only two or three substitution parameters.
After getting confused, I decided to just have a 3 argument substitution.
The three argument substitution only substitutes if both the variable name and the variable value match.

This is great but it doesn't follow the completeness theorem.
The iki_read should also handle the general case in addition to the specific case.

Provide a two argument substitution called "replace" that handles the more general case.
When any variable name matches the given replace parameter, then the variable value is replaced for all matching variable names regardless of the existing variable value.

Fix small mistakes in the IKI specification.
I needed to refer to the "variable value" with this change and "variable variable" is simply not the correct way.
Use "variable names" rather than "object names" to be more consistent and clear in this regard.