added draw method to circuit

[JamesB-1qbit]

Uses cirq's SVGCircuit such that the following code

from tangelo.linq import Circuit, Gate

circ = Circuit([Gate("CRZ", target=0, control=[1,2], parameter=1),
                Gate("CNOT", target=0, control=1),
                Gate("RZ", target=0, parameter=0.3)])
circ.draw()

makes
output.svg.pdf

[ValentinS4t1qbit]

Thank you for this simple solution, James. Since Cirq is a requirement of Openfermion, itself a requirement of our package, I think this is a very reasonable default solution.

When I try to call the draw method in the basics notebook, I get a bunch of warning for a font not found, in my Ubuntu environment. I think 1 warning line per text box, which will quickly get unbearable. Is there any way we can silence those warnings or not having them come up in the first place ?

[JamesB-1qbit]

I don't see these warnings and my virtual box seems to be broken. But I think that

warnings.filterwarnings("ignore", message=".*findfont.*")

I will commit this change and then someone who uses linux can test it. This error shows up on a bunch of cirq notebooks.

[ValentinS4t1qbit]

Thank you !