Little Enhancements

[michiruf]

Hi there,

I just stumbled across this composer extension because I wanted a minimal dev setup to run my nested library locally. It really works great and so I wanted to share a little feedback:

1. It did not work when neither the vendor directory and the composer.lock existed, maybe because the composer package I want to include is not shared on packagist yet? I got Your requirements could not be resolved to an installable set of packages.
2. Linking local libraries seems to happen only on the second pass or after an update, is that correct? Is that maybe because I specified your lib in require-dev?
3. Specifying a concrete dependency and its path would be a considerable addition to the functionality
4. Include information about how to debug
5. When I use the local repo plugin with an existing library on packagist, it seems always the packagist variant is resolved
6. Updating the readme slightly for usage examples as well as mentioning edge cases like above would help alot

Thanks alot!