More work on Model template

Add code to initialise `iter` Series object.

Add `iter` to `results` DataFrame in get_results().

Add code to return `values` as a Series object in
get_endogenous_variable_values().

Add code to handle output files.
Add output-file handling to fsic-build.py

Add output-file handling to fsic-build.py (differs slightly from Model
template owing to only one argument allowed).
Update README.md

Update README.md with required dependency on `pandas` (and `NumPy`) and
optional dependency on `IPython`.