Add beam part option "Use Endpoint Offsets"

When checked, the beam will use the endpoint part's position offset and
angle offset to determine where the endpoint of the beam should be,
instead of ignoring them. Default is off (to retain current behaviour on
existing costumes)
Merge pull request #63 from suchipi/patch-beam_part_use_endpoint_offsets

Add beam part option "Use Endpoint Offsets"