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/SmartDashboard/Sendable.h

@@ -12,6 +12,8 @@
 
 #include "tables/ITable.h"
 
+namespace frc {
+
 class Sendable {
  public:
   /**
@@ -31,3 +33,5 @@ class Sendable {
    */
   virtual std::string GetSmartDashboardType() const = 0;
 };
+
+}  // namespace frc