0.2.0

• Updated the top level classes to take a PhaseGroup instead of a
  List<List<Phase>>.
• Added logic to handle nested package directories.
• Basic windows support added, although it may still be unstable.
• Significantly increased the resolving speed by using the same sources cache.
• Added a basic README.
• Moved the .build folder to .dart_tool/build. Other packages in the future
  may also use this folder.