Merge branch 'md_PRD' into GSOC-Integrator
Hand over some calc_accel arguments using struct pointer
- should be faster
- more compact call and easy access to all configuration values if needed without clutter in the function call
Add option for stationary centered bodies
- useful for testing algorithms and physics
- all bodies will be kept at (0,0,0)
Change option for stationary centered bodies to runtime option
- uses function pointers for spkezp_c
- easier to control
- does not seem to harm performance
Merge branch 'GSOC-Integrator' into md_PRD
Changes aiming to improve accuracy of PRD
- Re-calculate speed vector during PRD calculation based on substep information