Use PEP8 naming

[EarlMilktea]

Description of the change:

Rename everything violating PEP8 naming convention.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 73.73913% with 151 lines in your changes missing coverage. Please review.

Project coverage is 76.26%. Comparing base (e15dee2) to head (0bc7d28). Report is 1 commits behind head on master.

Files	Patch %	Lines
graphix/visualization.py	3.37%	86 Missing :warning:
graphix/gflow.py	69.72%	33 Missing :warning:
graphix/pattern.py	88.39%	21 Missing :warning:
graphix/transpiler.py	95.23%	6 Missing :warning:
graphix/graphsim/basegraphstate.py	66.66%	2 Missing :warning:
graphix/sim/tensornet.py	66.66%	2 Missing :warning:
graphix/channels.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #199 +/- ## ========================================== + Coverage 76.19% 76.26% +0.06% ========================================== Files 37 37 Lines 5739 5739 ========================================== + Hits 4373 4377 +4 + Misses 1366 1362 -4 ```

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[shinich1]

@EarlMilktea thanks! please make sure docs build without error, and add a line or two to CHENGELOG.md.

[EarlMilktea]

@shinich1 Done!

[shinich1]

@EarlMilktea please add in [unreleased] part.