Rewrite the project README (#475)

This commit provides a much-needed update to the `README.md` of
wit-bindgen. The README now mentions WIT, components, the current
tooling workflow, and an updated "tutorial" for languages like Rust and
C. Overall it's intended to generally be more useful and up-to-date.

This commit additionally updates to the latest ABI for `wit-component`
and fixes a few minor issues here and there with the CLI.

Author: alexcrichton

Cargo.toml

@@ -27,7 +27,7 @@ indexmap = "1.9.1"
 wasm-encoder = "0.22.0"
 wat = "1.0.56"
 wit-parser = "0.4.1"
-wit-component = "0.4.3"
+wit-component = "0.4.4"
 
 wit-bindgen-core = { path = 'crates/bindgen-core', version = '0.3.0' }
 wit-bindgen-gen-guest-c = { path = 'crates/gen-guest-c', version = '0.3.0' }