Namespace all wpilibc functions/classes into "frc" namespace. (#311)

Base.h provides a backwards compatibility shim (enabled unless
NAMESPACED_WPILIB is defined) that does a "using namespace frc".
However, as some header files do not include Base.h, this may
be a breaking change in some corner cases (with an easy fix).

Fixes #218.

wpilibc/athena/src/SensorBase.cpp

@@ -11,6 +11,8 @@
 #include "HAL/HAL.h"
 #include "WPIErrors.h"
 
+using namespace frc;
+
 const int SensorBase::kDigitalChannels = HAL_GetNumDigitalChannels();
 const int SensorBase::kAnalogInputs = HAL_GetNumAnalogInputs();
 const int SensorBase::kSolenoidChannels = HAL_GetNumSolenoidChannels();