Switch to tracing for logging and add new example for IG API

Replaced `println!` with `tracing` macros for consistent and structured logging. Added dependencies `serde_json` and `tracing` to `Cargo.toml`. Introduced a new example, `ig.rs`, showcasing integration with the IG API. Updated library version to `0.1.2` in `Cargo.toml` and documentation.

Author: joaquinbejar

README.md

@@ -81,7 +81,7 @@ To use this SDK in your Rust project, add the following dependency to your `Carg
 
 ```toml
 [dependencies]
-lightstreamer-rs = "0.1.1"
+lightstreamer-rs = "0.1.2"
 ```
 
 ### Usage