Allow Users to Completely Disable webpack-hot-client

[shellscape]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

There have been repeated requests to completely disable all HMR functionality for webpack-serve. While that kind of defeats the purpose of the top-to-bottom setup, it's obvious folks are using this for it's bindings to webpack-dev-middleware in lieu of HMR.

This PR introduces support for setting hot: false instead of an Object, and the --no-hot-client CLI flag. The result is that webpack-hot-client will never be instantiated through koa-webpack, no WebSocket serve will be started, and the user will be responsible for loading changes tracked by webpack.

Breaking Changes

None

Additional Info

[codecov]

Codecov Report

Merging #50 into master will increase coverage by 0.14%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #50      +/-   ##
==========================================
+ Coverage   92.04%   92.19%   +0.14%     
==========================================
  Files           7        7              
  Lines         264      269       +5     
==========================================
+ Hits          243      248       +5     
  Misses         21       21

Impacted Files	Coverage Δ
cli.js	96.77% <ø> (ø)	⬆️
lib/options.js	87.8% <100%> (+0.79%)	⬆️

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