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/include/InterruptableSensorBase.h

@@ -13,6 +13,8 @@
 #include "HAL/Interrupts.h"
 #include "SensorBase.h"
 
+namespace frc {
+
 class InterruptableSensorBase : public SensorBase {
  public:
   enum WaitResult {
@@ -48,3 +50,5 @@ class InterruptableSensorBase : public SensorBase {
   HAL_InterruptHandle m_interrupt = HAL_kInvalidHandle;
   void AllocateInterrupts(bool watcher);
 };
+
+}  // namespace frc