style: move documents into libs

[jtr109]

resolve #10

[codecov]

Codecov Report

Merging #11 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #11   +/-   ##
=======================================
  Coverage   98.92%   98.92%           
=======================================
  Files           3        3           
  Lines          93       93           
=======================================
  Hits           92       92           
  Misses          1        1           

Impacted Files	Coverage Δ
kth_largest/src/lib.rs	100.00% <ø> (ø)
reverse_integer/src/lib.rs	100.00% <ø> (ø)
three_sum/src/lib.rs	97.95% <ø> (ø)

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