allow a negative distance argument. Improved documentation.
allow a negative distance argument. Improved documentation.

russpowers/Nim,dom96/Nim,russpowers/Nim,russpowers/Nim,russpowers/Nim,russpowers/Nim,dom96/Nim,dom96/Nim,dom96/Nim,dom96/Nim,russpowers/Nim,dom96/Nim,russpowers/Nim,dom96/Nim