Feature request: copyDirs

It could be useful to have an ability to specify directories to copy with its content to destination directory, similar to current functionality - copyFiles parameter.

It could be separate package.json parameter copyDirs or just enhancement of existing copyFiles - to take directories as well as files.

Use case

Library dlangui has resources directory which should be copied to the same directory where executable which is using library is located.
E.g., in library, there is res folder.
When I specify "copyFiles": {"res"} in package.json, DUB will copy its content into subdirectory with the same name res in directory with library user's executable.