similar does not accept colons as indices

[jishnub]

This attempts to get around #122 by explicitly preventing colons being passed to similar. This means that the StackOverflowError now becomes a MethodError

julia> oa = OffsetArray(rand(3,3), 0:2, 0:2)
3×3 OffsetArray(::Array{Float64,2}, 0:2, 0:2) with eltype Float64 with indices 0:2×0:2:
 0.339644  0.584673  0.474432
 0.689602  0.65758   0.673912
 0.920069  0.360913  0.917047

julia> similar(oa, Float64, (:,:))
ERROR: MethodError: no method matching similar(::OffsetArray{Float64,2,Array{Float64,2}}, ::Type{Float64}, ::Tuple{Colon,Colon})

[codecov]

Codecov Report

Merging #126 into master will decrease coverage by 1.71%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
- Coverage   86.17%   84.45%   -1.72%     
==========================================
  Files           2        2              
  Lines         188      193       +5     
==========================================
+ Hits          162      163       +1     
- Misses         26       30       +4     

Impacted Files	Coverage Δ
src/OffsetArrays.jl	86.84% <ø> (-2.28%)	⬇️

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[timholy]

Thanks! This is a good fix. Just needs a test.

FYI, motivated partly by #87 I've begun to rethink Julia's similar dispatch chain. That's delicate work because we can't break compatibility, and I ran short on time before I could finish that. But my preliminary guess is that ultimately we'll need to delete more types from those accepted by this similar method.