As many open source projects have started doing it, we're removing the
current year from the copyright notice, so that we don't need to bump
it every year.
It seems like only the first year of publication is technically
relevant for copyright notices, and even that seems to be something
that many companies stopped listing altogether (in a version controlled
codebase, the commits are a much better source of date of publication
than a hardcoded copyright statement).
We also now list Godot Engine contributors first as we're collectively
the current maintainers of the project, and we clarify that the
"exclusive" copyright of the co-founders covers the timespan before
opensourcing (their further contributions are included as part of Godot
Engine contributors).
Also fixed "cf." Frenchism - it's meant as "refer to / see".
The main change is to caculate tangent directly from bezier curve, without going
through discretized polyline, avoiding pitfalls of discretization. A similar refacor
had been applied to Curve3D.
The test cases for Curve2D is updated, comparing floating point with is_equal_approxmiate()
instead of `==`, in order to avoid float precision problem.
