Update the change log

Author: thewizardplusplus

CHANGE_LOG.md

@@ -1,5 +1,30 @@
 # Change Log
 
+## [v1.3.1](https://github.com/thewizardplusplus/luaplot/tree/v1.3.1) (2026-09-02)
+
+- models:
+  - 2D plot:
+    - storing limits as a `Range` from the [luamath](https://github.com/thewizardplusplus/luamath) library;
+    - iterating over points represented as `Vector2D(index, value)` from the [luamath](https://github.com/thewizardplusplus/luamath) library;
+    - copying mutable constructor and factory inputs;
+  - distance limit:
+    - fixing the class name from `Point` to `DistanceLimit`;
+  - 2D plot, 2D oscillogram, and distance limit:
+    - exposing a class name and a stringified representation via the [luaserialization](https://github.com/thewizardplusplus/luaserialization) library;
+    - generating a JSON Schema via the `schema()` static method;
+    - constructing an instance from serializable options via the `from_options()` static method;
+- global operations:
+  - supporting both sequences and objects with the `__index` metamethod in the `iterators` package;
+  - calculating the vertical difference between points represented as `Vector2D` objects;
+- refactoring:
+  - replacing the internal `types` package with the [luatypechecks](https://github.com/thewizardplusplus/luatypechecks) library;
+  - replacing the internal `maths` package and the CPML library with the [luamath](https://github.com/thewizardplusplus/luamath) library;
+  - adding the [luaserialization](https://github.com/thewizardplusplus/luaserialization) library;
+- misc.:
+  - adding GitHub Actions workflows for tests, linting, and documentation deployment;
+  - supporting Lua 5.1, 5.2, 5.3, 5.4, 5.5, and LuaJIT;
+  - improving the generated documentation.
+
 ## [v1.3](https://github.com/thewizardplusplus/luaplot/tree/v1.3) (2021-03-08)
 
 - global operations: