v0.7.0

Added

• Support for the ~ home directory symbol. All filenames are passed through the
  os.path.expanduser function.
• IPv4NetworkField now support setting a minimum and maximum prefix length, in bits.
• Field.help attribute to document the field, similar to a docstring. The help and
  autogenerated short_help attribute, can be used in UI to display information and
  documentation about the field.
• BaseSchema.generate_argparse_parser method to autogenerate an argparse.ArgumentParser
  object to parse command line arguments.
• Field.env and Schema.env to control automatically loading configuration values from
  environment variables.

Changed

• Improved error reporting with the ValidationError exception that contains the offending
  field's full name and path.