Validation warnings now stored in state object

This will allow for additional processing before actually triggering the
warnings. For the sake of this commit, though, we just keep with existing
functionality.
Warning no longer issued when overriding weak method appearing later in dfn obj
Began implementing virtual trait methods

These require special treatment with proxying.
Simplified ClassBuilder.buildMembers params

This cuts down on the excessive parameter length and opens up room for
additional metadata generation. Some slight foreshadowing here.
Added virtual members to class metadata

There does not seem to be tests for any of the metadata at present; they are
implicitly tested through various implementations that make use of them.
This will also be the case here ("will"---in coming commits), but needs to
change.

The upcoming reflection implementation would be an excellent time to do so.
Initial trait virtual member proxy implementation

This has some flaws that should be addressed, but those will be detailed in
later commits; this works for now.
Moved closure out of getMemberVisibility

This was defining a function on every call for no particular reason other
than being lazy, it seems.

Performance poopoo.
[bug fix] Corrected bug with implicit visibility escalation

See test case comments for details. This wasted way too much of my time.
Added test case for visibility escalation internally

For completeness, since this is how I originally observed the issue fixed in
the previous commit.
Began testing class subtyping with mixins
Objects are now considered types of class's mixed in traits

This is a consequence of ease.js' careful trait implementation that ensures
that any mixed in trait retains its API in the same manner that interfaces
and supertypes do.
Subtype mixin support
Added support for mixing in traits using use method on a base class
Added immediate partial class invocation support after mixin
Named classes now support mixins
Began named trait implementation

Does not yet support staging object like classes
Class.use now creates its own class
Began Scala-influenced linearization implementation

More information on this implementation and the rationale behind it will
appear in the manual. See future commits.

(Note the TODOs; return values aren't quite right here, but that will be
handled in the next commit.)
Trait method return value implementation correction and testing
Trait can now implement interfaces

Note the incomplete test case: the next commit will introduce the ability
for mixins to override methods that may have already been defined.