Support curl/wget instead of reqwest to support system proxy/reduce binary size

[mokeyish]

The integration of reqwest is pretty good at the moment, but I found that it doubles the space required for a simple program because it has a lot of dependencies.

Two cargo features, download-system and download-reqwest , could be added to allow choosing between them.

Each platform already has its own download tool, such as curl or wget. If self-update can automatically select and use them, there are two advantages:

1. Reduce binary size
2. Suppoert system proxy via ENV: HTTP_PROXY=http://proxy.example.com

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If these library are implemented, it may be possible to import it for use.

• Support curl/wget instead of reqwest to support system proxy/reduce binary size rs-videos/siwi-download#1
• Support curl/wget instead of reqwest to support system proxy/reduce binary size Jupiee/rawst#20

[jaemk]

Hey @mokeyish , I'm open to it. There was a PR (#117 ) opened a while ago that was never fully finished. I'm not sure when I I'll get the chance to either fix up that PR or redo it from scratch, but you're welcome to if you have the time

[mokeyish]

It looks like a heavy workload. I'll take a look at it and deal with it later when I have time. It probably won't be possible in the near future.