Add option --baseurl to allow running behind a reverse proxy

[vi]

Overriding base URL from / to other value modifies all links in directory listings to begin from custom location instead of just /.

This allows using simple-http-server behind a reverse proxy that maps only request from a website's "subdirectory" to simple-http-server.

Example nginx config snippet:

location /filemanager/ {
    rewrite /filemanager/(.*) /$1 break;
    proxy_pass http://127.0.0.1:7682/;
    proxy_request_buffering off;
    proxy_buffering off;
}

This pull request also includes #49.

[micwoj92]

This branch has conflicts that must be resolved

[vi]

@micwoj92 Rebased, also fixed redirect when uploading files.

[micwoj92]

Thank you @vi , a screen-oriented text editor software application.

[stappersg]

git remote add vi https://github.com/vi/simple-http-server
git fetch vi
git cherry-pick ffbae85d8337997cc741

I have now this merge request in my fork

[vi]

Is three a specific reason why this can't be upstreamed?

[TheWaWaR]

Suggested change

	.long("baseurl")
	.long("base-url")

[TheWaWaR]

Suggested change

	baseurl: String,
	base_url: String,

[TheWaWaR]

Is three a specific reason why this can't be upstreamed?

Sorry for so late reply, just don't have much time to test.

Please also rebase the code.

[vi]

Done.

[TheWaWaR]

Thanks!