Guy Fawkes "House on Fire" edition 2016

• bug fix in Elements/gdsii_arc.m
• a method (or indexing) that accesses an element property returns [] if an element does not have a requested
  property instead of throwing an error.
• improved 'subsref' methods for gds_library and gds_structure objects that enable more complex indexing operations. It is now possible, e.g., to write S(10).xy to get the xy record of the 10th element in a structure without having to copy the element first. In Octave it is also possible to use expressions such as L(10)(20).layer to get the layer number of the 20th element in the 10th structure of library L (this does not work in Matlab because double indexing is not permitted).
• update to Clipper library version 6.4