Row reading reworks

- Removed distinction between row and owning_row
- Changed semantics for fetch_one to row& + bool
- Renamed all fetch_* fns to read_*
- Added row.clear()

example/unix_socket.cpp

@@ -74,7 +74,7 @@ void main_impl(int argc, char** argv)
     boost::mysql::unix_resultset result = conn.query(sql);
 
     // Get all the rows in the resultset
-    std::vector<boost::mysql::owning_row> employees = result.fetch_all();
+    std::vector<boost::mysql::row> employees = result.read_all();
     for (const auto& employee: employees)
     {
         print_employee(employee);
@@ -88,7 +88,7 @@ void main_impl(int argc, char** argv)
 
     // Check we have updated our poor intern salary
     result = conn.query("SELECT salary FROM employee WHERE first_name = 'Underpaid'");
-    auto rows = result.fetch_all();
+    auto rows = result.read_all();
     ASSERT(rows.size() == 1);
     double salary = rows[0].values()[0].get<double>();
     ASSERT(salary == 10000);