reduce dependency on StaticArrays

[daanhb]

This PR demonstrates that we could have StaticArraysCore as a dependency rather than StaticArrays.

I'm not sure I like it, but it does reduce load time by more than 50%. In any case this is a breaking change, because one would have to load StaticArrays in addition to DomainSets in order to do anything in more than one dimension.

[daanhb]

#91

[codecov]

Codecov Report

Base: 85.83% // Head: 85.83% // No change to project coverage 👍

Coverage data is based on head (897dd1e) compared to base (b2341a8).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #131   +/-   ##
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  Coverage   85.83%   85.83%           
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  Files          31       31           
  Lines        2626     2626           
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  Hits         2254     2254           
  Misses        372      372           

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[jishnub]

This is probably not a good idea given the way the package is designed at present, and the breakages that this would lead to. In any case, the way ahead in this direction should be by making StaticArrays a weak dependency and defining a package extension for it. StaticArraysCore is somewhat obsolete with package extensions becoming a feature.