Add left division operator for matrix and vector

[KeitaNakamura]

This function may be out of scope of this package, but it's convenient.

[codecov-io]

Codecov Report

Merging #41 (6ff20ce) into main (5afe3e5) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
+ Coverage   94.01%   94.08%   +0.06%     
==========================================
  Files          12       12              
  Lines         802      811       +9     
==========================================
+ Hits          754      763       +9     
  Misses         48       48              

Impacted Files	Coverage Δ
src/ops.jl	99.59% <100.00%> (+0.01%)	⬆️

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