Add advanced examples to docs

[adrhill]

Adds three examples:

1. Generating ordered dithering algorithms from signed distance functions (SDFs)
2. Creating animations by color cycling
3. Hiding two images in one IndirectArray

Also makes color scheme generation accessible as DitherPunk.get_colorscheme when Clustering.jl is loaded

[codecov[bot]]

Codecov Report

Merging #58 (baf3f1f) into master (8b1ea58) will increase coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #58      +/-   ##
==========================================
+ Coverage   96.77%   96.81%   +0.03%     
==========================================
  Files          14       14              
  Lines         248      251       +3     
==========================================
+ Hits          240      243       +3     
  Misses          8        8              

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

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[adrhill]

I will remove Plots tomorrow :)

[adrhill]

Uploading the contour plot here to link to it.