A huge change in syntax.

+ `(:= (fname param ...) expr)` is replaced by `(= fname param ... expr)`
+ `(:= (name) const)` is replaced by `(= name const)`
+ `(-> (param ...) expr)` is replaced by `(^ param ... expr)`
+ `=` for equality check is replaced by `=?`

All the examples and tests are up to date with this change.