cargo new defaults to a binary project

cargo new will now default to generating a binary, rather than a library.We try to keep Cargo’s CLI quite stable, but this change is important, and isunlikely to cause breakage.

For some background, cargo new accepts two flags: —lib, for creatinglibraries, and —bin, for creating binaries, or executables. If you don’tpass one of these flags, it used to default to —lib. At the time, we madethis decision because each binary (often) depends on many libraries, and sowe thought the library case would be more common. However, this is incorrect;each library is depended upon by many binaries. Furthermore, when gettingstarted, what you often want is a program you can run and play around with.It’s not just new Rustaceans though; even very long-time community membershave said that they find this default surprising. As such, we’ve changed it,and it now defaults to —bin.