Made some changes to simplify usage
Do NOT delete existing post processing directories

This was a big time-waster when trying to gather results
incrementally.
Added utitility to convert a contour file to VTK file

Contour files are defined as

<TOTAL POINTS> <TOTAL REGIONS>
<POINTS IN REGION>
x1 y1 z1
x2 y2 z2
...
<POINTS IN REGION>
x1 y1 z1
x2 y2 z2
...
Added utility to plot age vs largest cross-sectional area