add changelog for 0.3

Author: kyren

CHANGELOG.md

@@ -1,3 +1,55 @@
+## [0.3]
+
+Huge release! Much safer `Executor` API that no longer requires recursion
+from Rust -> Lua -> Rust for Rust callbacks to call Lua functions, eliminating
+problems with unrestricted Rust stack usage. The `Executor` API also has a
+bunch more weird powers that other implementations of Lua can't have, like "tail
+resuming" other coroutines and "tail yield".
+
+There is a new `piccolo-util` crate that adds support for some very common use
+cases that are not trivial to do in `piccolo` proper:
+
+* Serde support for convenient conversion between Rust types and Lua tables.
+* "Freeze" system to safely support the common case where you need to pass
+  a non-'static (and non-'gc) value into Lua. Not specific to piccolo, it is
+  actually a general way of safely erasing a single lifetime parameter from a
+  type (and replacing it with a runtime check).
+* Super quick and simple way to wrap Rust types into a Lua userdata with
+  methods.
+
+`piccolo-util` will always be an **optional** dependency, and it may contain
+code that is more opinionated or limited than vanilla `piccolo` should be.
+`piccolo-util` will have opionions about things, and those opinions may be
+different than yours... if it is in your way or incomplete for your use, you can
+always use it as a starting point for something better.
+
+Also includes a lot of quality of life API improvements, error message
+improvements, and more!
+
+- New `Executor` API that enables safe thread recursion and "tail resume" /
+  "tail yield".
+- New `piccolo-util` crate with very commonly requested, useful features that
+  are too opinionated or limited to belong in `piccolo` proper.
+- API changes to `Stack` to support a single, unified thread stack shared
+  between Lua and callbacks, similar to PUC-Rio Lua et al.
+- Upvalues no longer keep entire threads alive and instead use new gc-arena
+  finalization support to become closed when threads are garbage collected.
+- `IntoMultiValue` / `FromMultiValue` conversion for tuples now allows every
+  element to be multi-converted rather than just the last element.
+- Support the `__eq` metamethod.
+- Error message improvements in lexer / parser errors (they now have line
+  numbers at least!).
+- API changes to second callback parameter, now an `Execution` type with `Fuel`
+  access *and* also calling thread information.
+- Add "chunk name" information to compiled chunks for future use in runtime
+  errors / tracebacks.
+- Simplified `ctx` access, most methods are now directly implemented on `Context`.
+- Lots of type renames for clarity, `AnyCallback` -> `Callback`, `AnyUserData`
+  -> `UserData`, `AnyValue` -> `Any`, and others.
+- Add line number annotations to opcodes for future tracebacks.
+- Clean up general ptr handling and allow the user to access internal `Gc`
+  pointers in all cases, allows for weak pointers to all pointer types.
+
 ## [0.2]
 - Allow `Thread` to be forcibly reset to a stopped state.
 - Improve the `Table` API, add functions that skip `IntoValue` conversion and