AboutCode v3.0.0.dev4

ABOUT files is now YAML formatted.
Supported license expression.
Supported JSON input and output format: #246 and #277
Support Python 3: #280
Refined help texts
Refined USAGE texts
Refined SPECs

Input key changes:

about_file is replaced by about_file_path
dje_license_key is replaced by license_expression
version is no longer a required field

API Updated:

• Break down the 3 major functions: inventory, genabout and genattrib into 3 subcommands:
  i.e.
  about inventory, about generate and about attrib

• A new check subcommand: #281

• Some options changes
  --extract_license becomes --fetch-license
--license_text_location becomes --license-notice-text-location

etc...