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.

wpilibcIntegrationTests/src/CircularBufferTest.cpp

@@ -11,6 +11,8 @@
 
 #include "gtest/gtest.h"
 
+using namespace frc;
+
 static const std::array<double, 10> values = {
     751.848, 766.366, 342.657, 234.252, 716.126,
     132.344, 445.697, 22.727,  421.125, 799.913};