SendableChooser generic value (#433)

* Java SendableChooser now decorates with type (non-breaking change)

* C++ SendableChooser now is templated on the type instead of using void* and stores values (breaking change)

* C++ SendableChooser now uses llvm::StringMap instead of std::map

wpilibc/shared/include/SmartDashboard/SendableChooserBase.h

@@ -0,0 +1,40 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2017. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <memory>
+#include <string>
+
+#include "SmartDashboard/Sendable.h"
+#include "tables/ITable.h"
+
+namespace frc {
+
+/**
+ * This class is a non-template base class for {@link SendableChooser}.
+ *
+ * It contains static, non-templated variables to avoid their duplication in the
+ * template class.
+ */
+class SendableChooserBase : public Sendable {
+ public:
+  virtual ~SendableChooserBase() = default;
+
+  std::shared_ptr<ITable> GetTable() const override;
+  std::string GetSmartDashboardType() const override;
+
+ protected:
+  static const char* kDefault;
+  static const char* kOptions;
+  static const char* kSelected;
+
+  std::string m_defaultChoice;
+  std::shared_ptr<ITable> m_table;
+};
+
+}  // namespace frc