Added intensity clamp transform

[mattwarkentin]

Fixes #347.

Description
Added torchio.ClampIntensity() transform according to discussions in #347 and #348. I chose to use the word "clamp" to be consistent with torch.clamp terminology (which is also the underlying implementation), but this can be changed according to your preference (e.g. clipping).

Added tests and all tests passed locally.

Checklist

• I have read the CONTRIBUTING docs and have a developer setup (especially important are pre-commitand pytest)
• Non-breaking change (would not break existing functionality)
• Breaking change (would cause existing functionality to change)
• Tests added or modified to cover the changes
• Integration tests passed locally by running pytest
• In-line docstrings updated
• Documentation updated, tested running make html inside the docs/ folder
• This pull request is ready to be reviewed
• If the PR is ready and there are multiple commits, I have squashed them and force-pushed

[codecov]

Codecov Report

Merging #622 (123fb3d) into master (6a91cff) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #622      +/-   ##
==========================================
+ Coverage   96.77%   96.79%   +0.02%     
==========================================
  Files         124      126       +2     
  Lines        6409     6466      +57     
==========================================
+ Hits         6202     6259      +57     
  Misses        207      207              

Impacted Files	Coverage Δ
tests/transforms/preprocessing/test_clamp.py	100.00% <100.00%> (ø)
torchio/transforms/__init__.py	100.00% <100.00%> (ø)
torchio/transforms/preprocessing/__init__.py	100.00% <100.00%> (ø)
...orchio/transforms/preprocessing/intensity/clamp.py	100.00% <100.00%> (ø)

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[fepegar]

Looking good. I've added some comments. I think I messed up and some comments went to the commit in your fork, instead of this PR. Can you see them?

[mattwarkentin]

Yep I can see all the comments. Will make these changes. Much of the unnecessary code is probably because I used RescaleIntensity as a template and so it needs refactoring now.

[fepegar]

Are you happy with my changes? Shall I merge?

[mattwarkentin]

LGTM! That's kind of you to check with me.

[fepegar]

Kind of you to contribute to an open-source project! Thanks again!