Move the codegen into its own crate

This makes the code generatioin reusable from third party crates.

pyo3-derive-backend/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "pyo3-derive-backend"
+version = "0.2.1"
+description = "Code generation for PyO3 package"
+authors = ["PyO3 Project and Contributors <https://github.com/PyO3"]
+homepage = "https://github.com/pyo3/pyo3"
+repository = "https://github.com/pyo3/pyo3.git"
+documentation = "http://pyo3.github.io/PyO3/pyo3/"
+categories = ["api-bindings", "development-tools::ffi"]
+license = "Apache-2.0"
+
+[dependencies]
+quote="0.3"
+log="0.4"
+
+[dependencies.syn]
+version="0.11"
+features=["full"]

pyo3-derive-backend/src/lib.rs

@@ -0,0 +1,21 @@
+// Copyright (c) 2017-present PyO3 Project and Contributors
+
+#![recursion_limit = "1024"]
+
+#[macro_use]
+extern crate log;
+#[macro_use]
+extern crate quote;
+extern crate syn;
+extern crate proc_macro;
+
+pub mod py_class;
+pub mod py_impl;
+pub mod py_proto;
+pub mod py_method;
+pub mod args;
+pub mod defs;
+pub mod func;
+pub mod method;
+pub mod module;
+pub mod utils;

pyo3cls/Cargo.toml

@@ -14,8 +14,10 @@ proc-macro = true
 
 [dependencies]
 quote="0.3"
-log="0.4"
 
 [dependencies.syn]
 version="0.11"
 features=["full"]
+
+[dependencies.pyo3-derive-backend]
+path = "../pyo3-derive-backend"

pyo3cls/src/lib.rs

@@ -5,24 +5,14 @@
 
 extern crate proc_macro;
 extern crate syn;
-#[macro_use] extern crate quote;
-#[macro_use] extern crate log;
+extern crate quote;
+extern crate pyo3_derive_backend;
 
 use std::str::FromStr;
 use proc_macro::TokenStream;
 
 use quote::{Tokens, ToTokens};
-
-mod py_class;
-mod py_impl;
-mod py_proto;
-mod py_method;
-mod args;
-mod defs;
-mod func;
-mod method;
-mod module;
-mod utils;
+use pyo3_derive_backend::*;
 
 
 #[proc_macro_attribute]