Add independent --analysis stage

[kmurray]

Currently the only way to re-do analysis (timing, power, area etc.) is to re-run the routing stage. However this may cause the routing implementation to change.

We should add support for performing analysis independently of routing. This would involve:

• Adding an --analysis option to control running analysis (similar to --pack/--place/--route)
• Separating the analysis code from routing
• Adding support for reading in the .route file produced by the routing stage

[kmurray]

As of ca8f27f VPR supports the --analysis option.

However VPR currently does not re-load the routing (from the .route file), so at the moment routing must still be performed before doing analysis.

[kmurray]

As of 8fe7c1e VPR supports re-loading routing (thanks to @wjiamin).

So the --analysis option should now works as desired.