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/src/Timer.cpp

@@ -15,6 +15,8 @@
 #include "HAL/HAL.h"
 #include "Utility.h"
 
+namespace frc {
+
 /**
  * Pause the task for a specified time.
  *
@@ -48,6 +50,10 @@ double GetTime() {
       .count();
 }
 
+}  // namespace frc
+
+using namespace frc;
+
 // for compatibility with msvc12--see C2864
 const double Timer::kRolloverTime = (1ll << 32) / 1e6;
 /**