Creating new sync Api for candle-hub.

- `api::Api` -> `api::tokio::api` (And created new `api::sync::Api`).
- Remove `tokio` from all our examples.
- Using similar codebase for now instead of ureq (for simplicity).

candle-hub/src/api/mod.rs

@@ -0,0 +1,6 @@
+/// The asynchronous version of the API
+#[cfg(feature = "tokio")]
+pub mod tokio;
+
+/// The synchronous version of the API
+pub mod sync;