First running implementation,
tests pending.
Correcting errors in the relativity formula, minor adjustments:
- make r_body direction clear in the local code of the function to avoid confusion
- bibcode for the paper that the formula is taken from
- #defines for beta and gamma in case someone wants to test different values
Merge branch 'md_relativity' into GSOC-Integrator
Merge branch 'master' into GSOC-Integrator
Merge branch 'GSOC-Integrator'