Mod.Doc is gone

Bye-bye, stubs. Just for now, not for ever.
Member.isJava is gone

Another stub bites the dust
removes semi-dummy implementations of some of the semantic APIs
this optimization at this point looks premature
Host.attrs now subsumes Host.defns and Host.owner
Host.parents now subsumes Host.overrides, same for Host.children and Host.overriding
Actually, I feel better when Host.owner and Host.attrs are split up
Arg => Term.Arg, Param.Type => Type.Arg, Pat.SeqWildcard => Pat.Arg.SeqWildcard
merges explicitss and implicits into paramss
removes most of Has.XXX traits

The only one which has proven to be really useful is Has.Template, which
has now become Member.Template.

Later on, when we get more experience with what convenience features we want
to provide in our API, we might reinstate some of the Has.XXX thingies.
removes the sketch of the overload resolution API

We'll need to have more experience with this before exposing this API.
It's not only value arguments. It might also be type arguments, implicits in scope, etc.
some simplification of semantic API
some classification of semantic APIs
trims the variety of Scopes to just Scope

The rest is gone into type classes in semantic APIs.

I would've completely removed Scope from the basic API, but that'd hurt
`def Tree.owner: Scope`. If Tree.owner returned just a Tree, that would
make it impossible to write `something.owner.members(...)`.
simplifies Scopes in semantic APIs

Let's just keep it as simple as possible before we actually get to
experiment with semantic APIs.
removal of `with Member.Type` from some `Member.Template`-returning methods was a mistake

Even though members don't have names, they still have Member.ref,
which returns Type.Ref for types and Term.Refs for terms. This extra precision
is important.
parameters redesigned. not quite what was planned though
removes Aux.TypeBounds
unification of parents and annotations
Aux.Self => Param.Term