add LBP circular implementation

[johnnychen94]

3x faster this time

using ImageFeatures
using LocalBinaryPatterns
using TestImages, ImageCore

img = float32.(testimage("camera"));

@btime lbp($img, 8, 4, lbp_original); # 39.790 ms (15 allocations: 2.00 MiB)
@btime lbp_original($img, 8, 2, $(Linear())); # 12.570 ms (12 allocations: 3.50 MiB)

# Constant interpolation is optimized by moving interpolation calculation out of the core loop
@btime lbp_original($img, 8, 2, $(Constant())); # 2.113 ms (10 allocations: 2.50 MiB)

future work: support npoints > 8 case.

[codecov]

Codecov Report

Merging #10 (5b72c17) into master (9418159) will decrease coverage by 0.34%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #10      +/-   ##
==========================================
- Coverage   96.77%   96.42%   -0.35%     
==========================================
  Files           3        3              
  Lines          62       84      +22     
==========================================
+ Hits           60       81      +21     
- Misses          2        3       +1     

Impacted Files	Coverage Δ
src/lbp_original.jl	100.00% <100.00%> (ø)
src/utils.jl	100.00% <100.00%> (ø)
src/compat.jl	0.00% <0.00%> (-33.34%)	⬇️

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