Improve error messages from network problems

[hypirion]

Currently, error messages caused by network problems when downloading dependencies are hard to read and understand. Although you can easily guess their cause, it should probably be a bit more readable.

[firesofmay]

@hypirion Hi, what kind of errors and errors messages you are expecting? What ns should I check to add this feature?

[dan-amoroso]

Hi, sorry for rehashing this old issue if it has been solved already, I am trying to find an easy entry-point to start contributing.

The current errors look like
Could not transfer artifact [...] from/to central (https://repo1.maven.org/maven2/): repo1.maven.org This could be due to a typo in :dependencies, file system permissions, or network issues. If you are behind a proxy, try setting the 'http_proxy' environment variable.

Which seems pretty good to me 👍 I imagine this has been done already? If not, what are the requirements for improving it?

Thanks in advance for your time and your work on leiningen