feat: support convert

[wolfogre]

close #18

[codecov]

Codecov Report

Merging #19 into master will increase coverage by 0.90%.
The diff coverage is 95.12%.

@@            Coverage Diff             @@
##           master      #19      +/-   ##
==========================================
+ Coverage   85.93%   86.84%   +0.90%     
==========================================
  Files           4        4              
  Lines         128      152      +24     
==========================================
+ Hits          110      132      +22     
  Misses          9        9              
- Partials        9       11       +2     

Impacted Files	Coverage Δ
internal/gtag/template.go	66.66% <ø> (ø)
test/internal/regular/empty_tag.go	83.33% <71.42%> (-16.67%)	⬇️
internal/gtag/gtag.go	84.61% <100.00%> (+0.94%)	⬆️
test/internal/regular/user_tag.go	100.00% <100.00%> (ø)

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