Implement DAY function

[stanim]

PR Details

Description

Returns the day of a date, represented by a serial number. The day is given as an integer ranging from 1 to 31.
https://support.microsoft.com/en-us/office/day-function-8a7d1cbb-6c7d-4ba1-8aea-25c134d03101

Syntax

DAY(serial_number)

The DAY function syntax has the following arguments:

• Serial_number Required. The date of the day you are trying to find. Dates should be entered by using the DATE function, or as results of other formulas or functions. For example, use DATE(2008,5,23) for the 23rd day of May, 2008. Problems can occur if dates are entered as text.

Related Issue

Fixes #1002

Motivation and Context

This helps with Excels from third party, where the DAY function is frequently used.

How Has This Been Tested

Added tests to calc_test.go

Tested on:

• OS: Archlinux 5.13.10-arch1-1
• WPS Spreadsheets (version wps-office 11.1.0.10702-1)
• LibreCalc (version libreoffice-fresh 7.1.5-2)

Types of changes

• Docs change / refactoring / dependency upgrade
• 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 read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

Codecov Report

Merging #1003 (fd47cc3) into master (dca03c6) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1003      +/-   ##
==========================================
+ Coverage   97.52%   97.55%   +0.03%     
==========================================
  Files          29       29              
  Lines       11222    11388     +166     
==========================================
+ Hits        10944    11110     +166     
  Misses        154      154              
  Partials      124      124              

Flag	Coverage Δ
unittests	97.55% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
calc.go	98.01% <100.00%> (+0.07%)	⬆️
date.go	100.00% <100.00%> (ø)

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[xuri]

Thanks for your PR, I have added date-time string parse support base on your branch.