Update CHANGELOG.md for release 0.3.3

[thierry-martinez]

The pre-release 0.3.3 failed to be published on PyPI because of the dependency to the not-yet-released graphix-qasm-parser. This was fixed in #373, and this commit updates the CHANGELOG.md with the changes merged since the pre-release, in order to keep the history linear.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.25%. Comparing base (9ebd775) to head (adc7070).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #376   +/-   ##
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  Coverage   86.25%   86.25%           
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  Files          44       44           
  Lines        6163     6163           
=======================================
  Hits         5316     5316           
  Misses        847      847           

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