add copy and othe single arg methods to force dispatch on parent type

[rafaqz]

also tweak sparse benchmarks, and benchmark copy

[codecov-io]

Codecov Report

Merging #13 into master will decrease coverage by 0.21%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master      #13      +/-   ##
==========================================
- Coverage   65.63%   65.42%   -0.22%     
==========================================
  Files          10       10              
  Lines         291      295       +4     
==========================================
+ Hits          191      193       +2     
- Misses        100      102       +2

Impacted Files	Coverage Δ
src/array.jl	45% <100%> (+1.41%)	⬆️
src/methods.jl	79.54% <33.33%> (-3.39%)	⬇️

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