Use project name from package.json instead of folder name for monorepo packages

[runspired]

Currently it uses the folder name instead of the package name, these are typically not the same.

[gilest]

If you have a packages folder and your projects in subfolders of that folder lerna-changelog will detect it and include the package names in the changelog for the relevant changes.

It would be nice if this feature also worked in monorepos that don't use a packages subdirectory.

Edit: Looks like this is being worked on in #294