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/shared/include/Buttons/JoystickButton.h

@@ -10,6 +10,8 @@
 #include "Buttons/Button.h"
 #include "GenericHID.h"
 
+namespace frc {
+
 class JoystickButton : public Button {
  public:
   JoystickButton(GenericHID* joystick, int buttonNumber);
@@ -21,3 +23,5 @@ class JoystickButton : public Button {
   GenericHID* m_joystick;
   int m_buttonNumber;
 };
+
+}  // namespace frc