- Archives now have a new metadata field 'comment'
- 'info' command shows a comment if it's present
- 'create' command now has option '--comment' for adding comments to archives.
- A new command 'comment' is added for modifying the comments on existing
archives.
Resolves#842.
the generation of those files was causing us way too much pain to
justify automatically generating them all the time.
those will have to be re-generated with `build_api` or `build_usage`
as appropriate, for example when function signatures or commandline
flags change.
see #384