This changes
- `.flag`, `.option`, `.options` and `.positionals` are now just fields
you access on the result of `parse` and `parseEx`.
- `clap.ComptimeClap` has been removed.
- `clap.StreamingClap` is now called `clap.streaming.Clap`
- `parse` and `parseEx` now takes a `value_parsers` argument that
provides the parsers to parse values.
- Remove `helpEx`, `helpFull`, `usageEx` and `usageFull`. They now just
expect `Id` to have methods for getting the description and value
texts.
