Change simulon target to simulon_gaussian

[jswinarton]

Context: The Xanadu Quantum Cloud simulator, formerly called simulon, now has the target name simulon_gaussian. This change was made to support many different simulon types in the future.

Description of the Change:

• References to simulon in documentation and tests have been changed to simulon_gaussian.
• A formatting change is made in strawberryfields/backends/gaussianbackend/gaussiancircuit.py. It appears that the black version on CI has been upgraded since the last commit, which now checks new elements in docstrings. This change has been made here instead of in a separate PR.

Benefits: People reading the docs will not try to submit jobs to a simulator that doesn't exist :slightly_smiling_face:

Possible Drawbacks: n/a

Related GitHub Issues: n/a

[codecov[bot]]

Codecov Report

Merging #576 (640def1) into master (3bb5657) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #576   +/-   ##
=======================================
  Coverage   98.38%   98.38%           
=======================================
  Files          75       75           
  Lines        8411     8411           
=======================================
  Hits         8275     8275           
  Misses        136      136           

Impacted Files	Coverage Δ
...fields/backends/gaussianbackend/gaussiancircuit.py	98.08% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 3bb5657...640def1. Read the comment docs.