coords2dihedrals.py now returns angles in the range from -180 to 180 by default

I changed the default branch-of-log for "coords2dihedrals.py" (from 0 to π). This means that now, by default the dihedral angles returned by this script are in the range from [-180,180) instead of [0,360). (This is a much more sensible choice for interpreting dihedral angles in molecules.) This can be overridden by supplying a number (in radians) representing the branch of log (a number from 0 to 2π) specifying where the discontinuity of the angle is located. (https://en.wikipedia.org/wiki/Complex_logarithm).