This change modifies destructors to anticipate that they can be called form a foreign thread if the GC is involved. The actual release of the reference will then happen deferred in the original thread.
The previous design, while intended as an improvement over the one-size-fits all Path struct of vibe-d:core, turned out to produce lots of bugs during the transition, because of missing Path.type checks.
The new design uses a cleaner approach, where the static type of a path value encodes the path format. An explicit cast is necessary to convert between different path types. The internet path type also performs proper validation and percent encoding, so that InetPath.toString() always produces a valid URI path.
This simplifies the logic by separating thread local notifications from cross-thread notifications, as well as replacing lockless operations by a spin lock. The thread local variant of ManualEvent is now also separated into a LocalManualEvent type.
The library is able to support simple TCP servers in the current state. The API is still mostly compatible with mainline vibe.d, but the driver systen has been replaced by the eventcore library and sockets/files/timers/... are now structs with automatic reference counting instead of GC collected classes. The stream interfaces have been removed for now.
