Support for crates with different library name

[jonasbb]

I tried to use the crate prettytable-rs in evcxr_jupyter, however I cannot get it to work. I think the problem is that even though the crate name is prettytable-rs, the library is only called prettytable (you use extern crate prettytable;).

Writing :dep prettytable-rs = "0.7" prints

can't find crate for `prettytable_rs`

on the terminal. Trying extern crate prettytable; results in the error

error: no matching package named `prettytable` found

being shown in the Jupyter notebook.

[davidlattimore]

Thanks for filing this. I didn't know it was possible to rename a library like that. It looks like it's possible to get the crate name by running "cargo metadata" after adding the dependency to Cargo.toml. e.g.:

 {
            "name": "prettytable-rs",
            "targets": [
                {
                    "kind": ["lib"],
                    "crate_types": ["lib"],
                    "name": "prettytable",
                },
            ],
}

So that would be one option to fix the :dep command.

As Celti mentioned on #21, we probably want to think about how this will look once 2018 is stable.

I suppose separating :dep and extern crate would fix this, albeit at the cost of users having to write both for every crate they import. Then later "use" instead of "extern crate".