Corrected the "short" model which is actually being called as a
subcircuit, not a resistor, from the extraction in magic. Also added
a new custom file "diode.spice" which does the same thing for the
diodes, which are defined as low-level diode types but are extracted
from magic as a subcircuit.
diff --git a/sky130/custom/models/short.spice b/sky130/custom/models/short.spice
index bc5faf0..30df356 100644
--- a/sky130/custom/models/short.spice
+++ b/sky130/custom/models/short.spice
@@ -1,2 +1,6 @@
* Resistor model "short" defined with a fixed resistance of 0.01 ohms.
.model short r r=0.01
+* If "short" is called as a subcircuit, then this needs to be supported, too.
+.subckt short 1 2 SUB l=0 w=0
+R0 1 2 short
+.ends
