[feat] Add support for Package.toml

[CrabNejonas]

Add support for a Package.toml file so that package related info has it's own place (and can be specified for non Cargo projects too)

This should also add a --config, -c flag to specify the config file.

The preferred order of resolution should be --config > Pacakger.toml > Cargo.toml and configurations should not be merged

[amr-crabnebula]

The resolution implemented in #15 is --config then Packager.{toml,json} combined with configs read from Cargo.toml . This allows for more flexibility IMO when configs are defined for different places in a single workspace.