'swift help' doesn't work

To implement command-line features like "swift build", the Swift driver treats swift <some name> as though you had written swift-<some name>. However, it does not respond sensibly to swift help package/build/test/etc. It would be better if it treated swift help <some name> as though you had written swift <some name> -help, and swift help <other args> as though you had written swift --help <other args>. (Pretty much all Swift executables handle -help; a few don't seem to handle -help.)

This can be implemented in swift-driver's swift-help executable, which is run if the user types "swift help <args>". The implementation of the tool can be found in the swift-driver repository: https://github.com/apple/swift-driver