Signal macro

Say goodbye to tedious and error prone boilerplate code. It is now
possible to trivially define signals emitte by Godot objects by using
the new #signal macro. Thanks to Pádraig Ó Cinnéide for his dedication
to this effort.

Improved Variant ergonomics

To accomplish the above signal support, Pádraig also upgraded the
Variant API, which is now a lot easier to use and with fewer special
APIs. Now rather than having type-aware initializer, you can just
create Variants from existing objects.

So you can now just do:

var myVector = Vector2 ()
var myVariant = Variant (myVector)

Convenience Vector operator APIs

Additional convenience operator overloads for vectors were contributed
by Matt mgshorter@gmail.com.

Fixes to @export

More documentation

OptionSets now get their own documentation (me)

Make documentation reflect recent improvements to linker settings
(much simpler now) by Alex Loren and Signals (me).

Alex also contributed updates to the documentation on how to build on
Windows.

API

VariantCollection and ObjectCollection now work as Swift collections,
so it is possible to iterate over them with for.

Mikhail Tishin did various updates to the generation of the API based
on the Json file that should assist writing additional tests,
extension and prepares us for a future where we support additional
modules.

New convenience APIs to register node paths by Marquis Kurt.

Export-ed properties now properly set the values of their backing
store. This issue was fixed by Airyzz 36567925+Airyzz@users.noreply.github.com
after he spotted the bug.

Tests

We now have some tests for the type layouts, to catch errors in the
future, contributed by Mikhail Tishin.