more useful rustpkg init

[minhnhdo]

This PR modifies the behavior of rustpkg init.

rustpkg init now accepts two more arguments, the first is the type of package to initialize (bin or lib), and the second is the package name. Instead of initializing a workspace in the current directory, rustpkg init now initializes a workspace under the directory with the same name as the supplied package name. In addition, it also creates some default crates (i.e. lib.rs or main.rs) under src/<package-name>/.

E.g. rustpkg init lib awesome_lib will create the following directory tree in the current directory.

awesome_lib/ 
 - bin/
 - build/
 - lib/
 - src/
    - awesome_lib/
       - lib.rs

The content of lib.rs is the following.

pub fn get_answer() -> int {
    42
}

EDIT: test.rs is no longer generated.
PS: re-opening of #10651, as per request @alexcrichton

[alexcrichton]

@mrordinaire, needs a rebase.

[emberian]

@mrordinaire needs another rebase. I also think init should be named to new-workspace or something along those lines, to save rustpkg init for something that actually sets up the recommend project structure (whatever that turns out to be).

[emberian]

Ok, reading the conversation on the other PR, init seems fine.