Support environment variable settings to download mirror

[lovelope]

Version
All
OS
macOS、Linux、Windows

Describe the bug
Like nvm, users can set the nodejs download mirror location.

NVM_NODEJS_ORG_MIRROR=https://npm.taobao.org/mirrors/node

Instead of adding additional plugins.
#24

[aooohan]

I'm thinking about this too. Because vfox is extended in the form of a plugin. I'm thinking about which way is more friendly:

1. Use environment variable settings as you mention.
2. Use additional plugins to represent the corresponding mirrors.

Plan 1) needs to be a place to explain how to use, how to configure. Plan 2) program more intuitive, users do not need to care about how to configure, just need to install the corresponding plugin on it. But additional plugins are needed.

[yimiaoxiehou]

I like Plan 2). This tools not only for nodejs，i want't remember a lots of env args like (NODE_MIRROR, GOLANG_MIRROR, JDK_MIRROR).

[yimiaoxiehou]

i hope can use vfox available to list mirror plugins .
it will implement this feature better.

vfox available can show flutter and flutter-cn now. maybe can add vfox available -u cmd to refresh list by version-fox-plugins

[yimiaoxiehou]

i hope can use vfox available to list mirror plugins . it will implement this feature better.

vfox available can show flutter and flutter-cn now. maybe can add vfox available -u cmd to refresh list by version-fox-plugins

em，vfox available can auto refresh by version-fox-plugins not need any arg。 😄
after my mirror plugin accept. it added in list.

@lovelope now, you can use vfox add nodejs/npmmirror --alias nodejs to use https://cdn.npmmirror.com (aliyun mirror) as node download source

[lovelope]

LGTM

[aooohan]

Looking at it this way, the original option 2 is more reasonable. ;)