Let jag download and run examples like 'go install' does

[kasperl]

Could we let 'jag run' and 'jag watch' start from URLs to make it really straightforward to try examples?

jag run https://github.com/toitlang/toit/blob/master/examples/hello.toit

Extra points if it could run examples from packages and automatically get the dependencies right.

[kasperl]

Maybe it actually makes even more sense now that we can install containers with services? We could do:

jag container install https://github.com/toitlang/pkg-service-foo

and add something to the pkg-service-foo package that would make it easy to identify the entry point, name, and possibly also the configuration options.