replace output annotations with the old prefix arguments

[ptwales]

• Remove the purs: and scala: annotations.
• Bring back the prefix arguments as a single -p,--prefix flag.
• Determine output path as prefix.folders.filename
  • What folders will be the path to the folder from some arbitrary root folder.
    • This might depend on being able to compile all templates in a folder as the root folder.
    • Different language implementations may modify the folders accordingly
      • scala lower cases the folders names.
      • purescript capitalizes the folder names.