#42 Add ability to freeze simulation on first error

[Daniel Quinz]

I am currently trying to debug a large sequential circuit and by the time I stop the clock after first seeing a red wire indicating an error, many subsequent transitions have occured, obscuring the first erronesous transistion.

It would be very helpful to be able to select a simulation option to freeze the simulation on the first error detected so that the circuit stae can be examined without further transitions obscuring the fault.

Related features would be the ability to add a 'breakpoint' widget that functions similar to a probe, except that it can specify stop simulation on signal input (true, false, rising/falling edge, bit value, clock count, or simulation step number). This would help greatly when trying to debug and/or validate a design.