Add serde_codegen and build script for stable Rust

This is necessary because stable Rust does not yet support custom #[derive]
implementations, which are needed for Serde's Serialize/Deserialize traits.

Serde has a macro package and compiler plugin which handle those, but compiler
plugins are *also* not availble in stable Rust, so we instead have to generate
code at build time using serde_codegen.

Bug for `custom_derive` feature: rust-lang/rust#29644

Bug for compiler plugins: rust-lang/rust#29597

Cargo.toml

@@ -2,6 +2,10 @@
 name = "ladaemon"
 version = "0.1.0"
 authors = ["Dirkjan Ochtman <[email protected]>"]
+build = "build.rs"
+
+[build-dependencies]
+serde_codegen = "0.7.10"
 
 [dependencies]
 docopt = "0.6.81"
@@ -14,7 +18,8 @@ rand = "0.3.14"
 redis = "0.5.3"
 router = "0.1.1"
 rustc-serialize = "0.3.19"
-serde_json = "0.7.0"
+serde = "0.7.10"
+serde_json = "0.7.1"
 time = "0.1.35"
 url = "1.1.0"
 urlencoded = "0.3.0"

build.rs

@@ -0,0 +1,16 @@
+// Stable Rust 1.9 doesn't support the custom_derive feature, so we generate
+// code for structures which #[derive] Serde's Serialize/Deserialize traits.
+
+extern crate serde_codegen;
+
+use std::env;
+use std::path::Path;
+
+pub fn main() {
+    let out_dir = env::var_os("OUT_DIR").unwrap();
+
+    let src = Path::new("src/lib.rs.in");
+    let dst = Path::new(&out_dir).join("lib.rs");
+
+    serde_codegen::expand(&src, &dst).unwrap();
+}