FTPlan times StridedArray

[jishnub]

Fixes #178. Now, the following works:

julia> v = rand(ComplexF64, 10);

julia> f = plan_leg2cheb(v);

julia> f * view(v, :) == f * v
true

I've conservatively required the arrays to be contiguous, as judged from their sizes and strides.

[codecov]

Codecov Report

Merging #179 (add1ee8) into master (8a82d79) will decrease coverage by 0.00%.
The diff coverage is 86.66%.

@@            Coverage Diff             @@
##           master     #179      +/-   ##
==========================================
- Coverage   78.79%   78.79%   -0.01%     
==========================================
  Files          13       13              
  Lines        2108     2117       +9     
==========================================
+ Hits         1661     1668       +7     
- Misses        447      449       +2     

Impacted Files	Coverage Δ
src/libfasttransforms.jl	77.94% <86.66%> (-0.01%)	⬇️

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