FIX : improve epilogue accessibility for workflow

[skoudoro]

The goal of this PR is to resolve #1344.

Now, epilog is setting up via the keyword References in workflow docstring.

[codecov-io]

Codecov Report

Merging #1353 into master will decrease coverage by 0.04%.
The diff coverage is 89.47%.

@@            Coverage Diff             @@
##           master    #1353      +/-   ##
==========================================
- Coverage   87.02%   86.98%   -0.05%     
==========================================
  Files         228      228              
  Lines       28841    29076     +235     
  Branches     3100     3134      +34     
==========================================
+ Hits        25099    25291     +192     
- Misses       3037     3072      +35     
- Partials      705      713       +8

Impacted Files	Coverage Δ
dipy/workflows/tests/workflow_tests_utils.py	100% <ø> (ø)	⬆️
dipy/tracking/metrics.py	81.12% <100%> (+0.09%)	⬆️
dipy/__init__.py	71.42% <100%> (+2.19%)	⬆️
dipy/tracking/streamline.py	97.95% <100%> (+0.01%)	⬆️
dipy/workflows/tests/test_iap.py	95% <100%> (+0.45%)	⬆️
dipy/workflows/base.py	79.41% <100%> (+0.46%)	⬆️
dipy/tracking/utils.py	86.93% <100%> (+0.03%)	⬆️
dipy/tracking/life.py	97.8% <100%> (+0.01%)	⬆️
dipy/core/geometry.py	90.29% <100%> (+0.03%)	⬆️
dipy/testing/__init__.py	77.77% <60%> (-6.84%)	⬇️
... and 4 more

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[Garyfallidis]

Hi @skoudoro, there is one minor comment.

[Garyfallidis]

Cool, thanks for the bug fix.