ENH: additional options for transforming points (closes #660)

- The -rotate-angle option allows convenient specification of a
  rotation about an arbitrary axis. Eg, -rotate-angle '((1 1 1) 45)'

- The -origin option can be used to temporarily shift the origin
  for the rotation operations. For example,

      -origin '(0 0 1)' -rotate-angle '((1 0 0) 180)'

  for mirroring.