Migrate CDataPack from a Compact Cassette tape. (#688)

* Migrate CDataPack from a Cassette Tape.

Tested-By: Headline22.

* Remove last IsReadable param pass.

* populate len still if CDataPack::ReadString is unreadable or the wrong type.

* Fyren Fixes(TM)(R)(C).

* Deprecate IDataPack.

core/sourcemod.cpp

@@ -619,7 +619,7 @@ unsigned int SourceModBase::GetGlobalTarget() const
 
 IDataPack *SourceModBase::CreateDataPack()
 {
-	return logicore.CreateDataPack();
+	return nullptr;
 }
 
 void SourceModBase::FreeDataPack(IDataPack *pack)