Add `replace` method to objects

[ortk95]

Adds a replace method to objects, to allow e.g. a new Body instance to be created with some parameters replaced:

body = planetmapper.Body('jupiter', '2020-01-01', observer='earth')
new = body.replace(utc='2020-01-01T12:34:56', observer='hst')
print(body)
# Body('JUPITER', '2020-01-01T00:00:00.000000', observer='EARTH')
print(new)
# Body('JUPITER', '2020-01-01T12:34:56.000000', observer='HST')

This also adds the corresponding __replace__ method to properly interface with the stdlib's copy.replace.

345

Pull request checklist

• [x] Add a clear description of the change
• [x] Add any new tests needed
• [x] Run spell check on new text visible to user (documentation, GUI etc.)
• [x] Check any changes to requirements.txt are reflected in setup.py and conda-forge feedstock
• [x] Check code passes CI checks (run run_ci.sh or check GitHub Actions)

See CONTRIBUTING.md for more details.

[coveralls]

Pull Request Test Coverage Report for Build 8722245095

Details

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.574%

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Totals
Change from base Build 8554926061:	0.0%
Covered Lines:	2894
Relevant Lines:	2906

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💛 - Coveralls