Add docs.

derive/src/lib.rs

@@ -1,3 +1,45 @@
+//! A derive macro for generation of simple `Externals`.
+//!
+//! ```nocompile
+//! #// no compile because we can't depend on wasmi here, or otherwise it will be a circular dependency.
+//! extern crate wasmi;
+//! extern crate wasmi_derive;
+//!
+//! use std::fmt;
+//! use wasmi::HostError;
+//! use wasmi_derive::derive_externals;
+//!
+//! #[derive(Debug)]
+//! struct NoInfoError;
+//! impl HostError for NoInfoError {}
+//! impl fmt::Display for NoInfoError {
+//!     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+//!         write!(f, "NoInfoError")
+//!     }
+//! }
+//!
+//! struct NonStaticExternals<'a> {
+//!     state: &'a mut usize,
+//! }
+//!
+//! #[derive_externals]
+//! impl<'a> NonStaticExternals<'a> {
+//!     pub fn hello(&self, a: u32, b: u32) -> u32 {
+//!         a + b
+//!     }
+//!
+//!     pub fn increment(&mut self) {
+//!         *self.state += 1;
+//!     }
+//!
+//!     pub fn traps(&self) -> Result<(), NoInfoError> {
+//!         Err(NoInfoError)
+//!     }
+//! }
+//! ```
+//!
+
+// We reached the `recursion_limit` in quote macro.
 #![recursion_limit = "128"]
 
 extern crate proc_macro;

src/host.rs

@@ -137,6 +137,8 @@ impl HostError {
 
 /// Trait that allows to implement host functions.
 ///
+/// You can use `wasmi-derive` or you can implement this trait manually.
+///
 /// # Examples
 ///
 /// ```rust

tests/derives.rs

@@ -1,3 +1,5 @@
+// If you are to update this code, make sure you update the example in `wasmi-derive`.
+
 extern crate wasmi;
 extern crate wasmi_derive;