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/Timer.h

@@ -10,6 +10,8 @@
 #include "Base.h"
 #include "HAL/cpp/priority_mutex.h"
 
+namespace frc {
+
 typedef void (*TimerInterruptHandler)(void* param);
 
 void Wait(double seconds);
@@ -51,3 +53,5 @@ class Timer {
   bool m_running = false;
   mutable priority_mutex m_mutex;
 };
+
+}  // namespace frc