Fix some docstrings

[stavros11]

While checking for ExecutionParameters, I found various leftovers, mainly in docstrings, which should have been updated to the new public API (and _core structure).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 52.08%. Comparing base (c0a2e42) to head (49133dc).
Report is 14 commits behind head on 0.2.

Additional details and impacted files

@@           Coverage Diff           @@
##              0.2    #1053   +/-   ##
=======================================
  Coverage   52.08%   52.08%           
=======================================
  Files          63       63           
  Lines        2803     2803           
=======================================
  Hits         1460     1460           
  Misses       1343     1343           

Flag	Coverage Δ
unittests	52.08% <ø> (ø)

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[alecandido]

Thanks, I've been quite negligent with docs and docstrings, so this is a clear improvement.

I expect even some further leftover, but we will incrementally improve tests and docs in future 0.2.x releases.