support hex dependencies when the path is not available

Right now publishing to hex a package that has path dependencies doesn't work. I propose to replace the publish command with the one from this plugin to allows it.

A custom version could also be used:
```
{myapp, {path, "path_to_my_app", {version, "X.Y.Z"}}}
```

If the version is unspecified the rebar.config will be edited with the current version before beeing published.

Start by examining the plugin's publish command and the rebar.config path-dependency examples in the issue. Check how publishing behaves when a path is unavailable, including the custom version form. Done means packages with path dependencies can be published to Hex, with the rebar.config version updated when no version is specified.

Written by the indexing model from the issue text.