Add float ordering float clause guards to changelog
- There is a `todo` keyword for type checking functions that have not yet been
implemented.
- Tuples can be indexed into using the `var.1` syntax.
+- `>.`, `>=.`, `<.`, and `<=.` operators are now supported in case clause guards
+ and can be used to check the ordering of floats.
## v0.7.1 - 2020-03-03
