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/DigitalSource.h

@@ -10,6 +10,8 @@
 #include "HAL/Types.h"
 #include "InterruptableSensorBase.h"
 
+namespace frc {
+
 /**
  * DigitalSource Interface.
  * The DigitalSource represents all the possible inputs for a counter or a
@@ -28,3 +30,5 @@ class DigitalSource : public InterruptableSensorBase {
   virtual bool IsAnalogTrigger() const = 0;
   virtual int GetChannel() const = 0;
 };
+
+}  // namespace frc