All `Signal` methods should be `final` because if they aren't it's impossible to add any signals into a derived class.
And yes, lets make `Signal` a `mixin template`.
* Removed gcstats. Garbage collector statistics will be avaialable in durintime's 'memory' module.
* Removed object.d. This module is replaced by the object.d provided by druntime.
* Removed std.array. To trap an array bounds error, import 'exception' from druntime and catch ArrayBoundsException.
* Removed std.asserterror. To trap an asertion failure, import 'exception' from druntime and catch AssertException.
* Removed std.gc. To interact with the garbage collector, import 'memory' from druntime.
* Removed std.hiddenfunc. No equivalent exception is currently exposed by druntime, but if one is exposed it will be called HiddenFuncException and be declared in 'exception'.
* Removed std.moduleinit. druntime declares ModuleInfo in object.d, so it is implicitly availble without importing.
* Removed std.outofmemory. To trap an out of memory error, import 'exception' from druntime and catch OutOfMemoryException.
* Removed std.switcherr. To trap a switch error, import 'exception' from druntime and catch SwitchException.
* Removed std.synchro. This functionality will exist within druintime.
* Removed std.thread. A Thread class is available within druntime's 'thread' module. An interface comparison will be provided separately.
* Removed std.typeinfo. The classes defined in this package are for runtime use and should not be visible to the user.
The prior version of Phobos has been archived in tags/phobos-2.019 if needed.
