Make build scripts more ergonomic

Fixes #19

README.md

@@ -32,17 +32,13 @@ Here's an example build.rs script:
 extern crate cbindgen;
 
 use std::env;
-use cbindgen::{Config, Library};
 
 fn main() {
-    let root = env::var("CARGO_MANIFEST_DIR").unwrap();
-    let config = Config::from_root_or_default(&root);
-
-    Library::load_crate(Path::new(root),
-                        "CRATE_NAME",
-                        &config)
-        .generate().unwrap()
-        .write_to_file("bindings.h");
+    let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
+
+    cbindgen::generate(crate_dir)
+      .unwrap()
+      .write_to_file("bindings.h");
 }
 
 ```

src/bindgen/mod.rs

@@ -51,5 +51,5 @@ mod writer;
 
 pub use self::cargo::*;
 pub use self::config::*;
-pub use self::library::Library;
+pub use self::library::{GeneratedBindings, Library};
 pub use self::cargo_toml::manifest;

src/lib.rs

@@ -14,3 +14,19 @@ extern crate toml;
 mod bindgen;
 
 pub use bindgen::*;
+
+use std::path::Path;
+
+/// A utility function for build scripts to generate bindings for a crate, using
+/// a `cbindgen.toml` if it exists.
+pub fn generate(crate_dir: &str) -> Result<GeneratedBindings, String> {
+    let crate_dir = Path::new(crate_dir);
+    Library::load_crate(Cargo::load(crate_dir, None)?,
+                        &Config::from_root_or_default(crate_dir))?.generate()
+}
+
+/// A utility function for build scripts to generate bindings for a crate with a
+/// custom config.
+pub fn generate_config(crate_dir: &str, config: &Config) -> Result<GeneratedBindings, String> {
+    Library::load_crate(Cargo::load(Path::new(crate_dir), None)?, config)?.generate()
+}