refactor: use babel on optimizations

[ramasilveyra]

• Pass the babel path instead of the raw string values in the nodes asts. Attribute, InterpolationEscaped, Condition and Iteration changed.
• Use the babel path to make the optimizations.
• Remove magic-string.

[codecov-io]

Codecov Report

Merging #9 into master will increase coverage by 1.67%. The diff coverage is 100%.

@@           Coverage Diff            @@
##           master     #9      +/-   ##
========================================
+ Coverage   98.32%   100%   +1.67%     
========================================
  Files          23     21       -2     
  Lines         657    598      -59     
  Branches      133    119      -14     
========================================
- Hits          646    598      -48     
+ Misses         11      0      -11

Impacted Files	Coverage Δ
src/code-generator-pug.js	100% <100%> (ø)	:arrow_up:
src/transformation.js	100% <100%> (ø)	:arrow_up:
src/optimize/dead-code-elimination-visitor.js	100% <100%> (+8.33%)	:arrow_up:
src/code-generator-ejs.js	100% <100%> (+6.94%)	:arrow_up:
src/traverser.js	100% <100%> (ø)	:arrow_up:
src/ast.js	100% <100%> (ø)	:arrow_up:
src/optimize/create-inlining-visitor.js	100% <100%> (ø)	:arrow_up:
src/optimize/evaluate.js	100% <100%> (+20%)	:arrow_up:
src/optimize/is-truthy.js	100% <100%> (+20%)	:arrow_up:

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