add std::move to optimize object construction

also fix clang warning: no out-of-line virtual method definitions by
moving destructor definition to .cpp file. By the way, make the
destructor pure virtual to make it abstract class.

src/async_manager.hpp

@@ -80,7 +80,7 @@ class nervana::async_manager : public virtual nervana::async_manager_source<OUTP
 {
 public:
     async_manager(std::shared_ptr<async_manager_source<INPUT>> source, const std::string& name)
-        : m_source(source)
+        : m_source(std::move(source))
         , m_state{async_state::idle}
         , m_name{name}
     {

src/interface.cpp

@@ -26,6 +26,8 @@ using namespace nlohmann;
 
 int IGNORE_VALUE;
 
+nervana::interface::config_info_interface::~config_info_interface() {};
+
 void json_configurable::verify_config(
     const std::string&                                          location,
     const vector<shared_ptr<interface::config_info_interface>>& config,

src/interface.hpp

@@ -74,7 +74,7 @@ namespace nervana
 class nervana::interface::config_info_interface
 {
 public:
-    virtual ~config_info_interface() {}
+    virtual ~config_info_interface()              = 0;
     virtual const std::string& name() const       = 0;
     virtual void parse(nlohmann::json js)         = 0;
     virtual bool        required() const          = 0;