RefinementRules to merge uniform_refine, barycentric_refine and spit_into functions

[chmerdon]

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Merges refine_uniform, refine_barycentric and split_into function into one function based on new RefinementRule type, also adding new uniform refinement types of triangles suitable for quadratic and cubic Lagrange interpolations.

[codecov-commenter]

Codecov Report

Patch coverage: 68.30% and project coverage change: -1.87 :warning:

Comparison is base (cf00976) 71.51% compared to head (7f4d67b) 69.65%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #26      +/-   ##
==========================================
- Coverage   71.51%   69.65%   -1.87%     
==========================================
  Files          24       24              
  Lines        3532     3572      +40     
==========================================
- Hits         2526     2488      -38     
- Misses       1006     1084      +78     

Impacted Files	Coverage Δ
src/ExtendableGrids.jl	100.00% <ø> (ø)
src/meshrefinements.jl	78.79% <68.30%> (-15.08%)	:arrow_down:

... and 2 files with indirect coverage changes

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