Fleshed out forward system and extensively documented its design considerations

Implemented and did basic tests on new IPluginFunction type
Split function types into a separate file

--HG--
extra : convert_revision : svn%3A39bc706e-5318-0410-9160-8a85361fbb7c/trunk%40182

core/systems/PluginSys.h

@@ -5,6 +5,7 @@
 #include <sh_list.h>
 #include <sh_stack.h>
 #include "sm_globals.h"
+#include "CFunction.h"
 
 using namespace SourceHook;
 
@@ -19,22 +20,6 @@ struct ContextPair
 	sp_context_t *ctx;
 };
 
-class CPlugin;
-
-class CFunction : public IPluginFunction
-{
-public:
-	CFunction(funcid_t funcid, CPlugin *plugin);
-public:
-	virtual int CallFunction(const cell_t *params, unsigned int num_params, cell_t *result);
-	virtual IPlugin *GetParentPlugin();
-public:
-	void Set(funcid_t funcid, CPlugin *plugin);
-private:
-	funcid_t m_funcid;
-	CPlugin *m_pPlugin;
-};
-
 class CPlugin : public IPlugin
 {
 	friend class CPluginManager;