Update changelog for hslua 0.9.0
## Changelog
+### 0.9.0
+
+- Added cabal flag to allow fully safe garbage collection: Lua garbage
+ collection can occur in most of the API functions, even in those usually not
+ calling back into haskell and hence marked as optimizable. The effect of this
+ is that finalizers which call Haskell functions will cause the program to
+ hang. A new flag `allow-unsafe-gc` is introduced and enabled by default.
+ Disabling this flag will mark more C API functions as potentially calling back
+ into Haskell. This has a serious performance impact.
+- `FromLuaStack` and `ToLuaStack` instances for lazy ByteStrings are added.
+- None-string error messages are handled properly: Lua allows error messages to
+ be of any type, but the haskell error handlers expected string values. Tables,
+ booleans, and other non-string values are now handled as well and converted to
+ strings.
+
### 0.8.0
- Use newtype definitions instead of type aliases for LuaNumber and LuaInteger.
