docs: update README and examples for v1.0.0

- Rewrite README with all new endpoints and current model names
- Add available models table with constructors
- Add FIM and OCR examples
- Update all examples for string-based Model type
- Update streaming example for Option<String> delta content
- Use serde_json::json!() for tool schemas in examples
- Add .envrc to .gitignore

examples/ocr.rs

@@ -0,0 +1,25 @@
+use mistralai_client::v1::{
+    client::Client,
+    constants::Model,
+    ocr::{OcrDocument, OcrRequest},
+};
+
+fn main() {
+    // This example suppose you have set the `MISTRAL_API_KEY` environment variable.
+    let client = Client::new(None, None, None, None).unwrap();
+
+    let request = OcrRequest {
+        model: Model::mistral_ocr_latest(),
+        document: OcrDocument::from_url("https://arxiv.org/pdf/2201.04234"),
+        pages: Some(vec![0]),
+        table_format: None,
+        include_image_base64: None,
+        image_limit: None,
+    };
+
+    let response = client.ocr(&request).unwrap();
+    for page in &response.pages {
+        println!("--- Page {} ---", page.index);
+        println!("{}", &page.markdown[..200.min(page.markdown.len())]);
+    }
+}