Vertex wip.
Came up with reasonable, but unworkable vertex impl.

This design is useful, but it cannot work because it means we can
add sources before sources and sinks after sinks.

We'll have to implement this as two sides - sinks and sources - then
the combinations, vertex.
Added shared/weak ptr equivalence comparisons.

shared/weak ptrs can be compared, but the syntax to do so is verbose.
This commit adds a simple equivalent() function that uses owner_before
to compare two smart pointers of compatible types, be they shared or
weak.

A predicate functor would be appropriate here as well.
Merge branch 'master' into vertex-wip
Vertex brainstorming successful.

Vertex has been split into sink and source, then inherits from both.
The graph-specific functionality should be complete for now.
Added rough def for MMC_UNREFERENCED.
Merge branch 'master' into vertex-wip
Renamed vertex->filter.
Refactored brainstorm into proper modules.

Used tcc because these classes will be templates as soon as audio
formats are decided.