feat(types): read ELEMENT_TYPE_VAR signature type

[tdakkota]

Fixes #36.

[codecov-commenter]

Codecov Report

Merging #41 (dbaaefd) into master (d92f9ee) will increase coverage by 0.53%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master      #41      +/-   ##
==========================================
+ Coverage   20.32%   20.86%   +0.53%     
==========================================
  Files          19       19              
  Lines        3163     3182      +19     
==========================================
+ Hits          643      664      +21     
+ Misses       2439     2435       -4     
- Partials       81       83       +2     

Impacted Files	Coverage Δ
cmd/printsig/find.go	0.00% <ø> (ø)
cmd/printsig/main.go	0.00% <0.00%> (ø)
types/element_type.go	25.00% <ø> (ø)
types/signature.go	53.48% <54.83%> (+4.27%)	⬆️

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