modified foerstner to return response image in line with other corner…

[zagerpatrick]

corner_foerstner was modified to return the Foerstner corner measure response image instead of the Foerstner corner measures which are currently returned. Fixes #4000

Description

Checklist

• Docstrings for all functions
• Gallery example in ./doc/examples (new features only)
• Benchmark in ./benchmarks, if your changes aren't covered by an
  existing benchmark
• Unit tests
• Clean style in the spirit of PEP8

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  doc/release/release_dev.rst.
• Consider backporting the PR with @meeseeksdev backport to v0.14.x

[pep8speaks]

Hello @zagerpatrick! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file skimage/feature/corner.py:

Line 645:80: E501 line too long (105 > 79 characters)

[jni]

@zagerpatrick thank you very much for helping with scikit-image! Unfortunately, we can't simply change the API here, since many users might be affected. Instead, we need to go through a deprecation cycle, as explained in our contributing document here:

https://scikit-image.org/docs/dev/contribute.html#deprecation-cycle

Please let us know if you would like more guidance in how to proceed.

[alexdesiqueira]

Thank you for your work @zagerpatrick! I left a small consideration here, too.

[alexdesiqueira]

I would put some default values for these two variables. How's the example values (0.5, 0.3) sound?

[alexdesiqueira]

Also, it would make more sense globally to have image, sigma, accuracy_thresh, roundness_thresh, since it'd maintain the model of the other functions. Then, we wouldn't need to deprecate the API. Is that right @jni?

[jni]

is that right @jni?

The arguments should indeed come after and be made keyword-only by using sigma=1, *, accuracy_thresh=..., but the API still needs to go through a deprecation cycle somehow, because the return value is being altered. I don't know what the best way to do this is...