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/PWMSpeedController.h

@@ -10,6 +10,8 @@
 #include "SafePWM.h"
 #include "SpeedController.h"
 
+namespace frc {
+
 /**
  * Common base class for all PWM Speed Controllers
  */
@@ -32,3 +34,5 @@ class PWMSpeedController : public SafePWM, public SpeedController {
  private:
   bool m_isInverted = false;
 };
+
+}  // namespace frc