Add option `--scan DIR` to `drom project` to scan for `package.toml` and add them

[lefessan]

[zapashcanon]

@lefessan, where would this package.json come from ? Esy ? Npm ? I never use any of these so I'm not familiar with them, but I can have a look. If you have a link to a repository using them, that would be helpful.

[lefessan]

I was referring to the package.json files created by drom itself. The idea is that you can create a new drom project by merging multiple drom projects (sub-modules, again), and you would just have to scan them.

I am now thinking about finding a better name for the package.json files, to avoid confusion with other tools like ezy/npm.

[lefessan]

Sorry, I made a mistake in the title, it's package.toml files that I was expecting drom to scan. So, there is actually no need to change the name, since it is different from package.json.