Add bits to circuit call method

[thisac]

• Upgrade circuit call to accept classical bits in which to store measurement values. If no bits are passed to the circuit call, measurements will not be stored when circuit is simulated.

  circuit = Circuit(2, 2)
  
  with circuit.context as (q, c):
      ops.Hadamard(q[0])
      ops.Hadamard(q[1])
      ops.Measurement(q) | c
  
  circuit_2 = Circuit(2, 2)
  
  with circuit_2.context as (q, c):
      circuit(q, c)  # pass bits to 'circuit'

• Fixes issue with circular import due to simulator and operations files importing each other (quick fix by moving import to inside sample method).

[codecov[bot]]

Codecov Report

Merging #34 (56ed3e2) into master (ce5df76) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #34   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           14        14           
  Lines         1215      1227   +12     
  Branches       191       197    +6     
=========================================
+ Hits          1215      1227   +12     

Impacted Files	Coverage Δ
dwave/gate/circuit.py	100.00% <100.00%> (ø)
dwave/gate/operations/base.py	100.00% <100.00%> (ø)

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