Added method for constructing RAG from image

[tejus-gupta]

Added a method for constructing region adjacency graph from an image. This RAG can be partitioned by any graph clustering method to segment the image.

I am unsure whether the documentation clearly explains how to use the function. @timholy Can you have a look?

[codecov[bot]]

Codecov Report

Merging #31 into master will decrease coverage by 31.11%. The diff coverage is 52.94%.

@@             Coverage Diff             @@
##           master      #31       +/-   ##
===========================================
- Coverage   99.15%   68.04%   -31.12%     
===========================================
  Files           7        9        +2     
  Lines         356      532      +176     
===========================================
+ Hits          353      362        +9     
- Misses          3      170      +167

Impacted Files	Coverage Δ
src/core.jl	69.36% <52.94%> (-30.64%)	:arrow_down:
src/region_merging.jl	50% <0%> (-41.67%)	:arrow_down:
src/felzenszwalb.jl	60% <0%> (-40%)	:arrow_down:
src/watershed.jl	63.41% <0%> (-32.89%)	:arrow_down:
src/meanshift.jl	69.23% <0%> (-30.77%)	:arrow_down:
src/fast_scanning.jl	75% <0%> (-25%)	:arrow_down:
src/region_growing.jl	76.92% <0%> (-23.08%)	:arrow_down:
src/clustering.jl	0% <0%> (ø)
src/ImageSegmentation.jl	0% <0%> (ø)

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[tejus-gupta]

I have made the requested changes.

I had earlier mistakenly created a new branch im2graph on this repository and pushed the code here directly. I have deleted this branch now and pushed the code correctly to my fork. I think the branch has been completely deleted from this repository. Can you check this?

[timholy]

Thanks so much! The branches seem fine.