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/include/command/MockCommand.h

@@ -9,6 +9,8 @@
 
 #include <Commands/Command.h>
 
+namespace frc {
+
 class MockCommand : public Command {
  private:
   int32_t m_initializeCount;
@@ -40,3 +42,5 @@ class MockCommand : public Command {
   int32_t GetInterruptedCount() { return m_interruptedCount; }
   bool HasInterrupted();
 };
+
+}  // namespace frc