Completed variable Inglis-Teller limit capability

- Added correct maths in Particle.cpp
- Updated FlyE.cpp to utilise this correctly

See ManifoldIntersect.nb for derivation of the maths...
Continued k-distribution capability and improved config file usage

- Continued with adding uniform distribution of ks (NEED TO PUT ITLIM
INSIDE LOOP)
- Changed most of the preprocessor directives to config file values;
some performance loss but easier to understand and control code
- Updated config file documentation