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/sim/include/simulation/SimContinuousOutput.h

@@ -21,6 +21,8 @@
 
 using namespace gazebo;
 
+namespace frc {
+
 class SimContinuousOutput {
  private:
   transport::PublisherPtr pub;
@@ -44,3 +46,5 @@ class SimContinuousOutput {
    */
   float Get();
 };
+
+}  // namespace frc