support modified LBP with average_mode

[johnnychen94]

using TestImages, ImageCore
using LocalBinaryPatterns
using ImageFeatures

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

# original + average: 4x faster
@btime modified_lbp($img, $lbp_original); # 23.296 ms (14 allocations: 2.00 MiB)
@btime lbp_original($average_mode, $img); # 5.409 ms (3 allocations: 256.16 KiB)

# interpolation + average: 1.8x faster
@btime modified_lbp($img, 24, 3, $lbp_original); # 225.435 ms (15 allocations: 2.00 MiB)
@btime lbp_original($average_mode, $img, 24, 2); # 120.412 ms (32 allocations: 2.00 MiB)

[codecov]

Codecov Report

Merging #13 (f4ccc68) into master (0031270) will increase coverage by 0.55%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #13      +/-   ##
==========================================
+ Coverage   94.44%   95.00%   +0.55%     
==========================================
  Files           5        5              
  Lines         108      120      +12     
==========================================
+ Hits          102      114      +12     
  Misses          6        6              

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

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