Ported Cal2jd

[prakharcode]

Test added for leap year and non-leap year.

[coveralls]

Pull Request Test Coverage Report for Build 180

• 14 of 14 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 87.404%

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Totals
Change from base Build 179:	0.5%
Covered Lines:	340
Relevant Lines:	389

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💛 - Coveralls

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@3712df7). Click here to learn what that means. The diff coverage is 100%.

@@            Coverage Diff            @@
##             master      #29   +/-   ##
=========================================
  Coverage          ?   86.49%           
=========================================
  Files             ?        7           
  Lines             ?      348           
  Branches          ?        0           
=========================================
  Hits              ?      301           
  Misses            ?       47           
  Partials          ?        0

Impacted Files	Coverage Δ
src/conversions.jl	100% <100%> (ø)

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