r10k-style Puppetfile compatibility

From the README

- Forge modules must be specified like this:

```
mod 'theforeman/puppet'
```

- Git modules must be specified like this:

```
mod 'apache',
  :git => 'https://github.com/puppetlabs/puppetlabs-apache.git'
```

It'd be nice to have support for all possibilities in r10k Puppetfiles to use g10k as a drop-in replacement