feat: egg-bin generate

[atian25]

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

• close https://github.com/eggjs/egg/issues/2723
• diff with RFC
  • argv not args
  • don't check pkg
  • loadUnit -> loadUnits

[codecov[bot]]

Codecov Report

Merging #101 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #101   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          11     12    +1     
  Lines         202    228   +26     
=====================================
+ Hits          202    228   +26

Impacted Files	Coverage Δ
lib/cmd/generate.js	100% <100%> (ø)
bin/egg-bin.js	100% <0%> (ø)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 4a8805e...162d2c3. Read the comment docs.

[atian25]

更新了一个版 @popomore @gxcsoccer

[atian25]

重新提交了，@popomore

[atian25]

这个先不合