v2.0.0

• No longer compatible with Python 2.
• @package decorator removed.
• Additional Part attributes can be specified when exporting libraries.
• Added unexpio dict to Interface objects for accessing I/O without buses expanded into individual nets.
• Added connect() and __iadd__() methods to interconnect Interface objects.
• Part libraries are pickled when first loaded for faster access on subsequent accesses.
  The directory for storing the pickled library files is specified in the SKiDL configuration file.
• The KICAD tool identifier now points to KICAD8.