npe2

napari plugin refactor

see also napari/napari#3115

Includes a command line tool npe2 with the following commands:

Commands:
  convert   Convert existing plugin repository to npe2 format (create manifest, update setup.cfg)
  parse     Show parsed manifest as yaml
  validate  Validate manifest for a distribution name or manifest filepath.

examples:

# convert current directory to an npe2-ready plugin
# (note: the repo must also be installed and importable in the current environment)
npe2 convert .

npe2 validate your-plugin-package

npe2 parse your-plugin-package