Added support of rest param `%&` and last positional param `%$` in short
lambdas. Example: `#(% .apply %$ %&)`.
Implemented Scala-like string interpolation via `(fmt)` macro. All strings with `$` inside are
converted to (fmt ...) on reader-stage level. For example   `"Hello, $name!"` is
converted to `(fmt "Hello, $name!")` and then expanded to `("Hello, " + name +
"!")`. Use `$$` for `$` escaping, and `$=var` for expanding var name as well as
var value. See more examples in `test/format.mjs`.