Automatically generate C header from Rust API (zcash#97)

* generate C header file on build using cbindgen

* add newlines

.gitignore

@@ -2,3 +2,4 @@
 **/*.rs.bk
 Cargo.lock
 .criterion
+**/libproofs.h

Cargo.toml

@@ -40,11 +40,13 @@ criterion = "0.2.3"
 tempfile = "3"
 proptest = "0.7"
 
+[build-dependencies]
+cbindgen = "0.6.0"
 
 [[bench]]
 name = "pedersen"
 harness = false
 
 [[bench]]
 name = "drgraph"
-harness = false
+harness = false

build.rs

@@ -0,0 +1,18 @@
+extern crate cbindgen;
+
+const VERSION: &'static str = env!("CARGO_PKG_VERSION");
+
+fn main() {
+    let crate_dir = std::env::var("CARGO_MANIFEST_DIR").unwrap();
+
+    let cfg = cbindgen::Config::from_root_or_default(std::path::Path::new(&crate_dir));
+
+    cbindgen::Builder::new()
+        .with_config(cfg)
+        .with_crate(crate_dir)
+        .with_header(format!("/* libproofs Header Version {} */", VERSION))
+        .with_language(cbindgen::Language::C)
+        .generate()
+        .expect("Unable to generate bindings")
+        .write_to_file("libproofs.h");
+}

cbindgen.toml

@@ -0,0 +1,3 @@
+[export]
+# A list of symbols to not include in the generated bindings
+exclude = ["MerkleTree"]