Add support for custom global state (#111)

* feat: add 'has_main_file' to App struct

* feat: handle custom state from the main.rs file

* feat: update tutorial template with new setup

* fix: apply clippy hints

* feat: add ApplicationState mention to documentation website

* feat: update version to v0.13.0

apps/documentation/src/routes/documentation/application-state.mdx

@@ -0,0 +1,55 @@
+import MetaTags from '../../components/meta-tags'
+
+<MetaTags
+  title="Tuono - Application state"
+  canonical="https://tuono.dev/documentation/application-state"
+  description="Learn how to add features to your Tuono application"
+/>
+
+import Breadcrumbs, { Element } from '../../components/breadcrumbs'
+
+<Breadcrumbs breadcrumbs={[{ label: 'Application state' }]} />
+
+# Application state
+
+The main reason Tuono is fast it's because it loads just the features that are needed for the project.
+
+To defined them you need to fill the `ApplicationState` struct in the `./src/main.rs` file and they will be automatically available
+in all the handlers you will define across the application.
+
+```rs
+// src/main.rs
+
+#[derive(Clone)]
+pub struct ApplicationState {
+    pub website_name: String,
+	pub base_path: String
+}
+
+pub fn main() -> ApplicationState {
+    let website_name = "tuono".to_string();
+    let base_path = "http://localhost:3000".to_string();
+
+    ApplicationState {
+        website_name,
+        base_path
+    }
+}
+```
+
+> For the sake of simplicity here we just enable a `String` but you can add Database connections or
+> HTTP clients (take a look [here](/documentation/tutorial/api-fetching) for an example with an HTTP client).
+
+Now the `ApplicationState` is available on all the handlers as following:
+
+```rs
+// src/routes/index.rs
+
+#[tuono_lib::handler]
+// The first argument always is the Request
+// The ApplicationState arguments are optional. You can use just the ones you need
+// to use in the handler (with no specific order).
+async fn my_handler(req: Request, website_name: String) -> Response {
+    ...
+}
+```

apps/documentation/src/routes/documentation/tutorial/api-fetching.mdx

@@ -28,7 +28,7 @@ Clear the `index.rs` file and paste:
 ```rust
 // src/routes/index.rs
 use serde::{Deserialize, Serialize};
-use tuono_lib::reqwest::Client;
+use reqwest::Client;
 use tuono_lib::{Props, Request, Response};
 
 const ALL_POKEMON: &str = "https://pokeapi.co/api/v2/pokemon?limit=151";
@@ -56,9 +56,73 @@ async fn get_all_pokemons(_req: Request, fetch: Client) -> Response {
 }
 ```
 
-> The first argument is always the request `req: Request` which contains the request data like the query parameters and the headers.
-> The rest of the arguments are optional and they don't need to be specified
-> if they are not used. Enabled out of the box a [Reqwest](https://docs.rs/reqwest/latest/reqwest/) HTTP client.
+> The first argument is always the request `req: Request` which contains all the request's data like the query parameters and the HTTP headers.
+> The rest of the arguments represents the [ApplicationState](/documentation/application-state) and are optional.
+
+The terminal will complain now for two reasons:
+
+1. We don't have imported any `reqwest` crate
+2. The second argument `fetch: Client` has not been defined yet as global state.
+
+Let's fix these in the next section.
+
+## Application state
+
+Compared to the common Javascript runtimes Tuono is fast because only the features you need for your project will be loaded.
+
+You can load them in the `ApplicationState` of your app inside the `./src/main.rs` file. This is the file that will be executed just once at the very beginning of your application.
+
+> For the tutorial we will use [Reqwest](https://docs.rs/reqwest/latest/reqwest/) which is one of the most famous HTTP library.
+
+To install it just run in your terminal:
+
+```bash
+$ cargo add reqwest
+```
+
+A new entry has just been added to your `Cargo.toml` file.
+
+```diff
+[package]
+name = "tuono"
+version = "0.0.1"
+edition = "2021"
+
+[[bin]]
+name = "tuono"
+path = ".tuono/main.rs"
+
+[dependencies]
+tuono_lib = "0.14.0" # the version might be different
+serde = { version = "1.0.202", features = ["derive"] }
+++ reqwest = "0.12.9" # the version might be different
+```
+
+> The `Cargo.toml` is the manifest file of your application in which handling the Rust's dependencies (similarly as the `package.json` for Javascript).
+
+Now let's define the `ApplicationState` in the `./src/main.rs` file.
+
+```rs
+// Import here the just added reqwest library
+use reqwest::Client;
+
+#[derive(Clone)]
+// Extend this struct with the feature you will need for your application
+pub struct ApplicationState {
+    // This will be available to all your route handlers
+    pub fetch: Client,
+}
+
+pub fn main() -> ApplicationState {
+    let fetch = Client::new();
+    return ApplicationState { fetch };
+}
+```
+
+Now the `fetch: Client` argument is available in the above defined handler and the terminal should not complain anymore.
+Let's see in the next section how to show the fetched data on the browser.
+
+## Handling the page UI
 
 Now the Pokémon are correctly fetched and hydrated on the client side, so we can actually use them. Clear the `index.tsx` file and paste: