Added a new pad type: trace pads, for antennas and other trace-like elements.

- layer.h (enum pad_type): added pad type pt_trace
- layer.c (pad_type_to_layers, layers_to_pad_type), inst.c (inst_pad):
  "trace" pad instantition and conversion infrastructure
- fpd.y (pad_type), dump.c (print_obj): .fpd file I/O for "trace" pads
- postscript.c (prologue): added Postscript function "horpath" to produce
  horizontal stripes
- postscript.c (hatch): show "trace" pads with horizontal stripes
- gui_style.h (gc_pad_trace), gui_style.c (gc_pad_trace, gui_setup_style),
  gui_inst.c (pad_gc): added visualization of "trace" pads
- gui_status.c (show_pad_type): added "trace" pad type
- README: added description of "trace" pads
- README: added usage examples for the various pad types



git-svn-id: http://svn.openmoko.org/trunk/eda/fped@5998 99fdad57-331a-0410-800a-d7fa5415bdb3

README

@@ -270,9 +270,17 @@ Type		Layers
 ---------	-------------------------------------
 (default)	copper, solder mask, and solder paste
 bare		copper and solder mask
+trace		copper without solder mask opening
 paste		solder paste
 mask		solder mask
 
+Typical uses:
+- "bare": connectors printed directly on the PCB
+- "trace": connections or antennas
+- "paste": sparse solder paste, e.g., for QFN center pads
+- "mask": non-standard mask openings, e.g., for solder mask defined
+  pads
+
 
 Rounded pads
 - - - - - -