Internal packages parsing support with a flag

[greenpart]

Describe the PR
Add --parseInternal flag to parse internal packages.

Related issue
#508

Additional context

[codecov-io]

Codecov Report

Merging #509 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #509      +/-   ##
=========================================
+ Coverage   86.78%   86.8%   +0.02%     
=========================================
  Files           7       7              
  Lines        1536    1539       +3     
=========================================
+ Hits         1333    1336       +3     
  Misses        119     119              
  Partials       84      84

Impacted Files	Coverage Δ
parser.go	82.14% <100%> (+0.04%)	⬆️
gen/gen.go	89.74% <100%> (+0.08%)	⬆️

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[easonlin404]

#508 (comment)

[codecov-commenter]

Codecov Report

Merging #509 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #509      +/-   ##
==========================================
+ Coverage   84.85%   84.88%   +0.02%     
==========================================
  Files           7        7              
  Lines        1869     1872       +3     
==========================================
+ Hits         1586     1589       +3     
  Misses        177      177              
  Partials      106      106              

Impacted Files	Coverage Δ
gen/gen.go	96.87% <100.00%> (+0.02%)	⬆️
parser.go	80.42% <100.00%> (+0.03%)	⬆️

---

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