Add first half of calibration example.

This is a Device wrapper struct that has methods and a get_serial() function.

examples/calibration.rs

@@ -0,0 +1,76 @@
+#![allow(non_upper_case_globals)]
+extern crate k4a_sys;
+use std::ptr;
+use std::ffi::{CString};
+use k4a_sys::*;
+
+struct Device {
+    idx : usize,
+    k4a_device: k4a_device_t,
+}
+//The beginnings of a wrapper struct
+impl Device {
+    pub fn get_idx(&self) -> usize {
+        self.idx
+    }
+
+    pub fn get_k4a_device(&self) -> k4a_device_t {
+        self.k4a_device
+    }
+
+    // pub fn get_k4a_device_mut_ptr(&self) -> *mut k4a_device_t {
+    //     (&self.k4a_device).as_raw()
+    // }
+    pub fn new(k4a_device: k4a_device_t, idx: usize) -> Self {
+        Self {
+            idx,
+            k4a_device,
+        }
+
+    }
+}
+fn open_device() -> Option<Device> {
+    unsafe {
+        let device_count = k4a_sys::k4a_device_get_installed_count();
+        let mut device: k4a_device_t = ptr::null_mut();
+        if device_count == 0 {
+            println!("No K4A devices found");
+            return None;
+        }
+
+        if k4a_device_open(0, &mut device) != k4a_buffer_result_t_K4A_BUFFER_RESULT_SUCCEEDED {
+            println!("Failed to open device");
+            return None;
+        }
+        Some(Device::new(device, 0))
+    }
+}
+
+fn get_serial(device: &Device) -> Option<String> {
+    unsafe {
+        let mut serial_number_length: usize = 0;
+
+        if k4a_device_get_serialnum(device.get_k4a_device(), ptr::null_mut(), &mut serial_number_length) != 
+            k4a_buffer_result_t_K4A_BUFFER_RESULT_TOO_SMALL {
+            println!("{}: Failed to get serial number length", device.get_idx());
+            return None
+        }
+
+        let mut serial_number = CString::new(vec![1u8; serial_number_length]).expect("Building a cstring failed");
+        let serial_number_ptr = serial_number.into_raw();
+
+        if k4a_device_get_serialnum(device.get_k4a_device(), serial_number_ptr, &mut serial_number_length) != 
+            k4a_buffer_result_t_K4A_BUFFER_RESULT_SUCCEEDED {
+                println!("{}: Failed to get serial number", device.get_idx());
+                return None;
+        }
+        serial_number = CString::from_raw(serial_number_ptr);
+        serial_number.into_string().ok() 
+    }
+}
+
+fn main () {
+    let device = open_device().expect("Couldn't open device");
+    let serial_number = get_serial(&device).expect("Couldn't get serial number");
+    println!("Found device with serial number {}", serial_number)
+}