feat: support register helper

[booxood]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

Support register helper

[codecov]

Codecov Report

Merging #8 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master     #8   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           2      2           
  Lines          28     37    +9     
=====================================
+ Hits           28     37    +9

Impacted Files	Coverage Δ
config/config.default.js	100% <ø> (ø)	⬆️
app.js	100% <100%> (ø)	⬆️

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[littledu]

@atian25 这个 PR 或者 register helper 的功能有准备实现吗？刚好用到这里的时候发现不支持