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/src/Buttons/InternalButton.cpp

@@ -7,6 +7,8 @@
 
 #include "Buttons/InternalButton.h"
 
+using namespace frc;
+
 InternalButton::InternalButton(bool inverted)
     : m_pressed(inverted), m_inverted(inverted) {}