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/Buttons/NetworkButton.h

@@ -12,6 +12,8 @@
 
 #include "Buttons/Button.h"
 
+namespace frc {
+
 class NetworkButton : public Button {
  public:
   NetworkButton(const std::string& tableName, const std::string& field);
@@ -24,3 +26,5 @@ class NetworkButton : public Button {
   std::shared_ptr<ITable> m_netTable;
   std::string m_field;
 };
+
+}  // namespace frc