💥 changed iterators to andom_access_iterator #593

This commit changes the iterator category to andom_access_iterator and allows offsets and subscript operators for object iterators.

test/src/unit-algorithms.cpp

@@ -240,9 +240,8 @@ TEST_CASE("algorithms")
             SECTION("sorting an object")
             {
                 json j({{"one", 1}, {"two", 2}});
-                CHECK_THROWS_AS(std::sort(j.begin(), j.end()), json::invalid_iterator&);
-                CHECK_THROWS_WITH(std::sort(j.begin(), j.end()),
-                                  "[json.exception.invalid_iterator.209] cannot use offsets with object iterators");
+                std::sort(j.begin(), j.end());
+                CHECK(j == json({{"one", 1}, {"two", 2}}));
             }
         }