This is technically redundant since it's equivalent to:
var f = Fn.new { ... }
But it seems worth adding if we're going to make functions and a
functional/procedural style intuitive and natural in Wren. It's a bit
of sugar, but it doesn't hurt much to add and makes the code read a
lot better.
Get rid of the separate opt-in IO class and replace it with a core
System class.
- Remove wren_io.c, wren_io.h, and io.wren.
- Remove the flags that disable it.
- Remove the overloads for print() with different arity. (It was an
experiment, but I don't think it's that useful.)
- Remove IO.read(). That will reappear using libuv in the CLI at some
point.
- Remove IO.time. Doesn't seem to have been used.
- Update all of the tests, docs, etc.
I'm sorry for all the breakage this causes, but I think "System" is a
better name for this class (it makes it natural to add things like
"System.gc()") and frees up "IO" for referring to the CLI's IO module.
* Eliminate "new" reserved word.
* Allow "this" before a method definition to define a constructor.
* Only create a default constructor for classes that don't define one.
