Created Crystal API (markdown)

Crystal-API.md

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+
+```rust
+use async_trait::async_trait;
+use alloc::{string::String, vec::Vec, boxed::Box};
+
+#[async_trait]
+pub trait Application {
+	fn new() -> Self;
+
+	async fn run(&mut self, _: Vec<String>) -> Result<(), Error> {
+		Ok(())
+	}
+}
+
+#[derive(Debug)]
+pub enum Error {
+	UnknownCommand(String),
+	CommandFailed(String),
+	ApplicationError(String),
+	EmptyCommand,
+}
+
+```