Value equality for MortalityTable types

[chris-b1]

This implements == for UltimateTable and SelectUltimateTable based on the underlying values and metadata.

[codecov]

Codecov Report

Merging #126 (b739e0e) into master (aa662ae) will increase coverage by 0.07%.
The diff coverage is 100.00%.

❗ Current head b739e0e differs from pull request most recent head f56fd8d. Consider uploading reports for the commit f56fd8d to get more accurate results

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
+ Coverage   90.63%   90.70%   +0.07%     
==========================================
  Files           9        9              
  Lines         395      398       +3     
==========================================
+ Hits          358      361       +3     
  Misses         37       37              

Impacted Files	Coverage Δ
src/MortalityTable.jl	96.72% <100.00%> (+0.16%)	⬆️

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[alecloudenback]

Thanks!