In this week, I have changed the Ptrace to handle multi-length wire-segment
FPGAs. I tested the program with two benchmarks and in both benchmarks Ptrace
gave the same delay as VPR did. More over, the updated version can handle 
not only multi-length wire segment with full buffer, but also can handle
the interconnect with pass transistor switch. 

Now I am cleaning up the delay variation part.