[Feature] detrend R-R intervals

[danibene]

Description

This PR aims to add the ability to detrend R-R intervals as a preprocessing step. See also #671 (comment)

Proposed Changes

I changed the intervals_preprocess() function so that it optionally calls signal_detrend() by passing detrend_method.

Checklist

• I have read the CONTRIBUTING file.
• My PR is targetted at the dev branch (and not towards the master branch).
• I ran the CODE CHECKS on the files I added or modified and fixed the errors.
• I have added the newly added features to News.rst (if applicable)

[DominiqueMakowski]

Could we add some examples here?

[DominiqueMakowski]

Awesome, last two little things; should we rename intervals_preprocess() to intervals_process() to maintain consistency with the other *_process() functions

Also, we can add th new exported function to the documentation

[codecov-commenter]

Codecov Report

Base: 52.65% // Head: 52.74% // Increases project coverage by +0.09% 🎉

Coverage data is based on head (0a394f8) compared to base (262cc00).
Patch coverage: 81.34% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #711      +/-   ##
==========================================
+ Coverage   52.65%   52.74%   +0.09%     
==========================================
  Files         277      279       +2     
  Lines       12588    12624      +36     
==========================================
+ Hits         6628     6659      +31     
- Misses       5960     5965       +5     

Impacted Files	Coverage Δ
neurokit2/misc/__init__.py	100.00% <ø> (ø)
neurokit2/hrv/hrv.py	42.55% <50.00%> (+2.12%)	⬆️
neurokit2/hrv/hrv_rqa.py	46.15% <50.00%> (+8.65%)	⬆️
neurokit2/hrv/hrv_utils.py	61.84% <75.00%> (-0.48%)	⬇️
neurokit2/hrv/hrv_nonlinear.py	64.59% <78.94%> (-0.51%)	⬇️
neurokit2/hrv/intervals_process.py	81.25% <81.25%> (ø)
neurokit2/hrv/intervals_utils.py	81.48% <81.48%> (ø)
neurokit2/hrv/__init__.py	100.00% <100.00%> (ø)
neurokit2/hrv/hrv_frequency.py	60.86% <100.00%> (-0.84%)	⬇️
neurokit2/hrv/hrv_rsa.py	94.76% <100.00%> (+2.54%)	⬆️
... and 7 more

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[DominiqueMakowski]

All good for me, feel free to merge!

[danibene]

All good for me, feel free to merge!

Awesome, is it fine for me to merge #710 first? Since this is based off of that one

[DominiqueMakowski]

Yup!