Checks for negative entries in close and normalise functions of codata.py

[sarahshi]

Description

I modified functions within codata.py to return a UserWarning for when negative values are in either the array for the close function or in the dataframe for the normalise function.

Related Issue

See enhancement described here:
#103

Motivation and Context

This is a small quality of life improvement for these functions.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[coveralls]

Pull Request Test Coverage Report for Build 9114710863

Details

• 14 of 15 (93.33%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 91.635%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pyrolite/comp/codata.py	14	15	93.33%

Files with Coverage Reduction	New Missed Lines	%
pyrolite/util/plot/interpolation.py	1	95.24%

Totals
Change from base Build 8074334577:	-0.03%
Covered Lines:	6211
Relevant Lines:	6778

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💛 - Coveralls

[morganjwilliams]

Just needs a little reordering for the below-zero replacement/warning and should be good to go.

[morganjwilliams]

Thanks @sarahshi, I'll merge this one in now.