Use generics to define Deque instance for a type

[gammazero]

Deque uses generics to create a Deque that contains items of the type specified. To create a Deque that holds a specific type, provide a type argument to New or with the variable declaration.

This is a breaking change.

[codecov-commenter]

Codecov Report

Merging #23 (78a8c72) into master (31c4a01) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #23   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          145       149    +4     
=========================================
+ Hits           145       149    +4     

Impacted Files	Coverage Δ
deque.go	100.00% <100.00%> (ø)

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