avoid dynamic dispatch in no_offset_view(::Array)

[jishnub]

This is a common case, so it might be worth the specialized method. Seems to cut down on allocations in certain applications, although the performance gain appears to be minimal.

On master:

julia> a = zeros(0:1000, 0:1000);

julia> function f(a)
       x = OffsetArrays.no_offset_view(a)
       sum(x[i] for i = 1:lastindex(x))
       end
f (generic function with 1 method)

julia> @btime f($a);
  1.701 ms (4 allocations: 96 bytes)

After this PR:

julia> @btime f($a);
  1.684 ms (0 allocations: 0 bytes)

Also uses Origin in the constructor to make it simpler.

[codecov]

Codecov Report

Merging #175 (04a67a0) into master (233a7b9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #175   +/-   ##
=======================================
  Coverage   99.23%   99.23%           
=======================================
  Files           4        4           
  Lines         261      262    +1     
=======================================
+ Hits          259      260    +1     
  Misses          2        2           

Impacted Files	Coverage Δ
src/OffsetArrays.jl	99.45% <100.00%> (+<0.01%)	⬆️

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[timholy]

Thanks!