Include sample code for creating from buffer

examples/open_buf.rs

@@ -0,0 +1,32 @@
+extern crate gexiv2_sys as gexiv2;
+extern crate libc;
+
+use std::ffi;
+use std::ptr;
+
+#[allow(dead_code)]
+fn main() {
+    unsafe {
+        let minipng = [137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 1,
+                       0, 0, 0, 1, 8, 0, 0, 0, 0, 58, 126, 155, 85, 0, 0, 0, 10, 73, 68, 65, 84,
+                       8, 215, 99, 248, 15, 0, 1, 1, 1, 0, 27, 182, 238, 86, 0, 0, 0, 0, 73, 69,
+                       78, 68, 174, 66, 96, 130];
+
+        let mut err: *mut gexiv2::GError = ptr::null_mut();
+        let metadata = gexiv2::gexiv2_metadata_new();
+
+        let ok = gexiv2::gexiv2_metadata_open_buf(
+            metadata, minipng.as_ptr(), minipng.len() as libc::c_long, &mut err);
+        if ok != 1 {
+            match ffi::CStr::from_ptr((*err).message).to_str() {
+                Ok(v) => panic!(v.to_string()),
+                Err(_) => panic!("Unknown error")
+            }
+        }
+
+        let mime_type_str_ptr = gexiv2::gexiv2_metadata_get_mime_type(metadata);
+        println!("{}", ffi::CStr::from_ptr(mime_type_str_ptr).to_str().unwrap());
+
+        gexiv2::gexiv2_metadata_free(metadata);
+    }
+}