Add fold kwarg for arrow.get

[nik-k11]

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• [x] 🧪 Added tests for changed code.
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Description of Changes

• Add fold kwarg for arrow.get.
• Remove getattr since Python 2.7/3.5 support is dropped.
• Make fold a keyword-only argument for Arrow.__init__ per this discussion.

Also please note the fold documentation in ArrowFactory.get. Basically, I only relay the fold kwarg into Arrow.fromdatetime and Arrow.__init__ calls.

Doesn't seem like using fold for timestamps, now calls or dates makes sense. But maybe it should be passed. What do you think?

Closes: #872

[codecov[bot]]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (4d68b9c) compared to base (74a759b). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

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