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/SimEncoder.h

@@ -16,6 +16,8 @@
 
 using namespace gazebo;
 
+namespace frc {
+
 class SimEncoder {
  public:
   explicit SimEncoder(std::string topic);
@@ -35,3 +37,5 @@ class SimEncoder {
   void positionCallback(const msgs::ConstFloat64Ptr& msg);
   void velocityCallback(const msgs::ConstFloat64Ptr& msg);
 };
+
+}  // namespace frc