Updates to get const correctness up to snuff for c++17

include/inc-core/dbinterface.hpp

@@ -38,9 +38,9 @@ namespace IRDB_SDK
 		public:
 			virtual ~DBinterface_t() {};
 
-			virtual void   issueQuery(string query)        = 0;
+			virtual void   issueQuery(const string& query)        = 0;
 			virtual void   moveToNextRow()                 = 0;
-			virtual string getResultColumn(string colname) = 0;
+			virtual string getResultColumn(const string& colname) = 0;
 			virtual bool   isDone()                        = 0;
 			virtual void   commit()                        = 0;
 

include/inc-core/pqxxdb.hpp

@@ -27,10 +27,10 @@ namespace IRDB_SDK
 		public:
 			virtual ~pqxxDB_t() { };
 
-			virtual void         issueQuery(string query)         = 0;
+			virtual void         issueQuery(const string& query)         = 0;
 			virtual void         issueQuery(stringstream & query) = 0;
 			virtual void         moveToNextRow()                  = 0;
-			virtual string       getResultColumn(string colname)  = 0;
+			virtual string       getResultColumn(const string& colname)  = 0;
 			virtual bool         isDone()                         = 0;
 			virtual void         commit()                         = 0;
 			virtual pqxx::connection&