Tags: olsonse/chimp

Adds arbitrary collision expressions;

Adds Inverse and Log cross section models;
Some initial code for three body interactions;
Some initial code for inelastic collisions;
Add threshold energies to Lotz, Constant, and VHS cross section models;
Add initial python interface to CHIMP database;

Improves extrapolation; Diameters auto-average for VHS/constant cross…

… sections.

Several other improvments.

Replaced olson-tools with xylose. Database can grow at runtime.

Lotz cross section model added. Portability improvements.

Uses new physical::calc::Driver (better).

small doc tweak