Fix broken URL and add 1D test

[paurierap]

README's Observable URL was broken due to changes on Makie's docs site. I added a preprocessor for Literate.jl to add multiple version-dependent URLs. Besides, the addition of 1D test contains a broken test concerning scatter and GLMakie (the test passes with CairoMakie).

[codecov-commenter]

Codecov Report

Merging #39 (4a6261f) into master (5abcd52) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #39   +/-   ##
=======================================
  Coverage   93.06%   93.06%           
=======================================
  Files           2        2           
  Lines         202      202           
=======================================
  Hits          188      188           
  Misses         14       14           

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