Refactor FrontEnds and update vertex4

[houpc]

No description provided.

[codecov-commenter]

Codecov Report

Attention: 50 lines in your changes are missing coverage. Please review.

Comparison is base (d9d591d) 56.05% compared to head (c9c441c) 54.75%.

Files	Patch %	Lines
src/frontend/GV.jl	37.50%	30 Missing ⚠️
src/computational_graph/tree_properties.jl	38.09%	13 Missing ⚠️
src/computational_graph/optimize.jl	55.55%	4 Missing ⚠️
src/computational_graph/graph.jl	72.72%	3 Missing ⚠️

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Additional details and impacted files

@@               Coverage Diff               @@
##           computgraph     #177      +/-   ##
===============================================
- Coverage        56.05%   54.75%   -1.30%     
===============================================
  Files               51       52       +1     
  Lines             4526     5037     +511     
===============================================
+ Hits              2537     2758     +221     
- Misses            1989     2279     +290     

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[dcerkoney]

Looks good to me, but I think we need to add some tests before merging.

[dcerkoney]

Looks good to me modulo a few docstring typos