Adds support for specifying kernels using StaticArrays

[zygmuntszpak]

Fixes https://github.com/JuliaImages/ImageFiltering.jl/issues/252

[codecov[bot]]

Codecov Report

Base: 78.62% // Head: 91.97% // Increases project coverage by +13.34% :tada:

Coverage data is based on head (7e2a965) compared to base (826df52). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #254       +/-   ##
===========================================
+ Coverage   78.62%   91.97%   +13.34%     
===========================================
  Files          12       12               
  Lines        1062     1657      +595     
===========================================
+ Hits          835     1524      +689     
+ Misses        227      133       -94     

Impacted Files	Coverage Δ
src/imfilter.jl	92.13% <ø> (+9.96%)	:arrow_up:
src/border.jl	92.46% <100.00%> (+27.83%)	:arrow_up:
src/models.jl	100.00% <0.00%> (ø)
src/kernel.jl	100.00% <0.00%> (+2.24%)	:arrow_up:
src/ImageFiltering.jl	68.75% <0.00%> (+4.46%)	:arrow_up:
src/extrema.jl	100.00% <0.00%> (+5.55%)	:arrow_up:
src/mapwindow.jl	86.45% <0.00%> (+12.84%)	:arrow_up:
src/borderarray.jl	93.33% <0.00%> (+13.67%)	:arrow_up:
src/specialty.jl	100.00% <0.00%> (+15.38%)	:arrow_up:
... and 4 more

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[zygmuntszpak]

@timholy Please could you take a look when you get a chance

[johnnychen94]

Sorry I missed this PR and the issue. Will check it ASAP.