This may fix the bug that's blocking Issue #2441.

Classes with dtors should compile now. Haven't yet tested
whether they actually run correctly.

Beginnings of support for #2295, though that won't be done until
there's more test cases and resources are removed.

this is the final part of #1273

Issue #2201.

Classes can have ty params now. So can methods inside classes.
That was probably true before, but now it should still work if you
call methods in a class that's defined in a different crate. Yay!

get_with_default (nee from_maybe) => get_default
with_option (nee maybe) => map_default
with_option_do (nee may) => iter

As per discussion of 21be1379

Most could use the each method, but because of the hack used to
disambiguate old- and new-style loops, some had to use vec::each.

(This hack will go away soon.)

Issue #1619

from_maybe => get_with_default
maybe => with_option
may => with_option_do

I know these names are kind of ridiculous, but it's the best I could think of.
Feel free to bikeshed. Closes #2081

All field or method references within a class must begin with "self." now.
A bare reference to a field or method in the same class will no longer
typecheck.

Allow writing self.f() within a class that has a method f. In a future
commit, this syntax will be required. For now, you can write either
self.f() or f().

I added a "privacy" field to all methods (whether class methods or not),
which allowed me to refactor the AST somewhat (getting rid of the
class_item type; now there's just class_member).

This change uses the same code for handling the "self" reference for
classes as is already used for impls/ifaces. This allows removing the
extra maybe_self_id argument (which was just for classes) to trans_closure
that I added before. I also rewrote the translation for class ctors so
that it doesn't generate new AST nodes (instead translating directly).

Also changed visit so that it visits class ctors correctly with visit_fn,
and changed typestate to not do return-checking when visiting a class ctor.

This prevents us from spilling locals more than once.

Closes #2040

Issue #1981

They mysteriously fail on Windows, and Niko assures me this code is about
be replaced anyway.

The difference went away.

With the assumption of monomorphization