Ergo CLI and Rust engine 0.1.0

New

• The first version of the Rust engine. It follows spec 0.3, so a policy says ergo_spec: v0.3, and it's experimental: anything in it may still change.
• ergo-policy-sentences reads check sentences, for lines, from lines and paths, without the engine.
• ergo-policy-engine builds the report and the violations from a policy, an input and params, as JSON.
• ergo-policy-cli is the ergo command, which prints the report or the violations from policy, input and params files in JSON or YAML.
• ergo-policy-wasm builds the report in a browser, from JSON text. It isn't published: it's built from the repository for the editor.
• ergo-policy-sentences-wasm reads check sentences in a browser, from and to JSON text. It isn't published either: it's built from the repository for the editor.
• A for item whose path goes on into a list item that isn't an object, null included, fails that item as not_an_object, as every and some do, where it failed as unusable.