support `transform` package option

[unscriptable]

curl 0.7.x supports the moduleLoader config option, but it's misplaced. It currently has to be in a package's config object:

curl({
    packages: [
        { name: 'foo', location: 'here/foo', main: 'bar'
            config: {
                moduleLoader: 'curl/loader/cjsm11'
            }
        }
    ]
});

We'd like to rename it to "transform", and the top level seems like a better place for it:

curl({
    packages: [
        { name: 'foo', location: 'here/foo', main: 'bar', transform: 'curl/loader/cjsm11' }
    ]
});

In a future release, we may allow multiple transforms, but this feature request is just for a single transform.

[briancavalier]

:+1:

[unscriptable]

This will be implemented differently in 0.8.