Add output directory option to archive extract

[davschne-unity]

Specifications:

• Optional arguments are added to UnityDataTools archive extract to set the output directory to :
  • long form: --output-path <directory path>
  • short form: -o <directory path>
• If the directory specified doesn't exist, the tool should create it.
• If no output directory is specified, the tool should extract the archive to a directory called archive in the current directory.
• When extracting an archive, its internal file structure (i.e. subdirectories) should be preserved, not flattened.