extend OffsetArrays.centered for AxisArray

[johnnychen94]

ImageFiltering.centered is now moved to OffsetArrays.centered (JuliaArrays/OffsetArrays.jl#169), this requires AxisArrays.jl to extend its method so that ImageFiltering is still working as usual.

The codes here originally live in https://github.com/JuliaImages/ImageFiltering.jl/blob/d4df16a6a130fa0f1573394172bb48e634b6e76a/src/ImageFiltering.jl#L96-L99

This change adds OffsetArrays as a dependency:

julia> @time using AxisArrays
# after: 0.252187 seconds (408.84 k allocations: 25.418 MiB, 3.28% gc time)
# before:  0.209274 seconds (329.24 k allocations: 19.370 MiB)

I do not have write permission to this repo so may need someone with write permission to review it. Or I could help do some regular maintenance on this package. cc: @mbauman @timholy

[johnnychen94]

bump :)

[codecov]

Codecov Report

Merging #196 (5936d54) into master (28e9beb) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #196      +/-   ##
==========================================
+ Coverage   89.31%   89.34%   +0.03%     
==========================================
  Files           7        8       +1     
  Lines         674      676       +2     
==========================================
+ Hits          602      604       +2     
  Misses         72       72              

Impacted Files	Coverage Δ
src/offsetarrays.jl	100.00% <100.00%> (ø)

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[johnnychen94]

For the record, to not adding an extra dependency to this package, I decided to add it in ImageAxes.jl for now (as a permitted pirate). We can go back when we have a first-class conditional loading mechanism.