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/Utility.h

@@ -46,8 +46,12 @@ bool wpi_assertNotEqual_impl(int valueA, int valueB, const char* valueAString,
 
 void wpi_suspendOnAssertEnabled(bool enabled);
 
+namespace frc {
+
 int GetFPGAVersion();
 int64_t GetFPGARevision();
 uint64_t GetFPGATime();
 bool GetUserButton();
 std::string GetStackTrace(int offset);
+
+}  // namespace frc