support more extensions and js source type

[gucong3000]

Closes: #29 #27

• exports extensions
• add support for more extensions
• add support for source type

[codecov]

Codecov Report

Merging #30 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #30   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          12     13    +1     
  Lines         283    285    +2     
=====================================
+ Hits          283    285    +2

Impacted Files	Coverage Δ
index.js	100% <ø> (ø)	⬆️
normal-opts.js	100% <100%> (ø)
syntax.js	100% <100%> (ø)	⬆️
parse.js	100% <100%> (ø)	⬆️
get-lang.js	100% <100%> (ø)	⬆️

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