include directories so that builds on mac os are successful across broader range os OS/machines

Fixes #103 by specifically including the directory where libproc.h is found, even though it seems some machines don't need to be told where to find it. If this causes problems for anyone then we can always back it out...

Author: jrabinow

build.rs

@@ -6,7 +6,7 @@ fn main() {
     let bindings = bindgen::builder()
         .header_contents("libproc_rs.h", "#include <libproc.h>")
         .layout_tests(false)
-        .clang_args(&["-x", "c++"])
+        .clang_args(&["-x", "c++", "-I", "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/"])
         .generate()
         .expect("Failed to build libproc bindings");