curieimu.hpp: Add pthread include to lib header

CurieIMU example includes curieimu.hpp, which uses pthread symbols but
does not include pthreads.h, and thus fails building.  The library
builds successfully because the source file includes the pthread
header before including curieimu.hpp.

    * Moved pthread.h include from src to header.

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/curieimu/curieimu.cpp

@@ -30,7 +30,6 @@
 #include <stdexcept>
 #include <unistd.h>
 #include <stdlib.h>
-#include <pthread.h>
 
 #include "curieimu.hpp"
 

src/curieimu/curieimu.hpp

@@ -26,6 +26,7 @@
 #pragma once
 
 #include <mraa/firmata.h>
+#include <pthread.h>
 #include <queue>
 
 #define FIRMATA_START_SYSEX                 0xF0