Add an option to filter results in parse.py
Fix bug in DampedOscillation where it returned infinite values

Parameter Beta was stored in an unsigned.

Turns out (-Beta * t) where Beta is unsigned but t is a double and the
result is a double gives something like (MAX_UINT - a)*t, ie a huge
positive number!
Parameter twiddling in ode examples
In parse.py add option to save figures
Fix bug in python exchange length function
Add two more stiff ode test functions