add Stillinger-Weber potential and prepare for Tersoff
split potential.c file into two (input, output)
rename PARABEL -> PARABOLA
Finish STIWEB implementation, might need some minor tweaks
finish tersoff implementation, only testing left to do
fix small bugs with tersoff and stiweb
minor cosmetic updates
small fixes
add more neighbor distances to regular neighbor table
 e.g. r^2, vector r
this transitions may have created a few bugs, needs checking
finish transition from dist (r/r) -> dist(r) and rdist(r) -> dist_r(r/r)
more code cleanup, indent properly
update manybody potentials to new standard
small bugfixes, rename volumen -> volume
major update of all utilities (rewrite in python)
clean up for next (unstable) release
fix compile errors