variable reader/writer

[cooper]

I would like the parser to keep track of where variables are defined and then a new component which can generate source code after changing the values of variables. The rest of the source would be otherwise unaltered.

It should:

1. Track start and end pos of variables as they currently exist.
2. Replace the text in that area with the newly generated values.
3. Adjust the position of vars after that to consider the newly inserted text (or just work backward to avoid this).
4. Add any new variables to the bottom–I guess–or to bottom of the top where the variables are normally put.