Update documentation to account for stable support (#218)

* Remove `#![feature(proc_macro_hygiene)]` from documentation

Closes #217

* Update comment about nightly vs stable

docs/content/getting-started.md

@@ -1,13 +1,17 @@
 # Getting started
 
-## Install nightly Rust
+## Which version of Rust?
 
-Maud requires the nightly version of Rust.
-If you're using `rustup`,
-see the [documentation][rustup]
-for how to install this version.
+While Maud works well
+on both stable and [nightly] versions
+of Rust,
+the error messages are slightly better
+on nightly.
+For this reason,
+it is recommended to develop using nightly Rust
+but test and deploy using stable.
 
-[rustup]: https://github.com/rust-lang/rustup.rs/blob/master/README.md#working-with-nightly-rust
+[nightly]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
 
 ## Add Maud to your project
 
@@ -29,8 +33,6 @@ maud = "*"
 Then save the following to `src/main.rs`:
 
 ```rust
-#![feature(proc_macro_hygiene)]
-
 extern crate maud;
 use maud::html;
 

docs/content/web-frameworks.md

@@ -21,8 +21,6 @@ maud = { version = "*", features = ["actix-web"] }
 Actix request handlers can use a `Markup` that implements the `actix_web::Responder` trait.
 
 ```rust
-#![feature(proc_macro_hygiene)]
-
 use maud::{html, Markup};
 use actix_web::{web, App, HttpServer};
 
@@ -56,8 +54,6 @@ maud = { version = "*", features = ["iron"] }
 With this feature enabled, you can then build a `Response` from a `Markup` object directly. Here's an example application using Iron and Maud:
 
 ```rust
-#![feature(proc_macro_hygiene)]
-
 use iron::prelude::*;
 use iron::status;
 use maud::html;
@@ -91,9 +87,6 @@ maud = { version = "*", features = ["rocket"] }
 This adds a `Responder` implementation for the `Markup` type, so you can return the result directly:
 
 ```rust
-#![feature(decl_macro)]
-#![feature(proc_macro_hygiene)]
-
 use maud::{html, Markup};
 use rocket::{get, routes};
 use std::borrow::Cow;
@@ -116,8 +109,6 @@ fn main() {
 Unlike with the other frameworks, Rouille doesn't need any extra features at all! Calling `Response::html` on the rendered `Markup` will Just Work®.
 
 ```rust
-#![feature(proc_macro_hygiene)]
-
 use maud::html;
 use rouille::{Response, router};