Replace using namespace in headers with explicit namespaces.

As part of:
lancaster-university/codal-microbit-v2#240

Other targets should also apply patches like
bdfa1ec to ensure they don't
depend on the header files having the `using namespace codal`
line.`

inc/NRF52ADC.h

@@ -42,15 +42,14 @@ DEALINGS IN THE SOFTWARE.
 //
 #define NRF52_ADC_DATA_READY     1
 
-
-using namespace codal;
-
 //
 // NRF52ADCChannel status codes
 //
 #define NRF52_ADC_CHANNEL_STATUS_ENABLED                0x10
 #define NRF52_ADC_CHANNEL_STATUS_CONNECTED              0x20
 
+namespace codal
+{
 class NRF52ADC;
 
 class NRF52ADCChannel : public DataSource
@@ -350,5 +349,6 @@ class NRF52ADC : public CodalComponent, public PinPeripheral
      */
     void configureSampling();
 };
+} // namespace codal
 
 #endif

inc/NRF52PDM.h

@@ -40,7 +40,8 @@ DEALINGS IN THE SOFTWARE.
 //
 #define NRF52_PDM_BUFFER_SIZE           512
 
-using namespace codal;
+namespace codal
+{
 
 class NRF52PDM : public CodalComponent, public DataSource
 {
@@ -103,5 +104,6 @@ class NRF52PDM : public CodalComponent, public DataSource
 
     void startDMA();
 };
+} // namespace codal
 
 #endif

inc/NRF52PWM.h

@@ -15,9 +15,8 @@
 #define NRF52PWM_PWM_PERIPHERALS    3
 #define NRF52PWM_PWM_CHANNELS       4
 
-
-using namespace codal;
-
+namespace codal
+{
 class NRF52PWM : public CodalComponent, public DataSink, public PinPeripheral
 {
 
@@ -153,5 +152,6 @@ class NRF52PWM : public CodalComponent, public DataSink, public PinPeripheral
     int tryPull(uint8_t b);
 
 };
+} // namespace codal
 
 #endif