Now that wgsl-analyzer 0.6 is released, most explicit type annotations on vec can be dropped (the exception being when it is a type conversion).
Also changes mix to select when the selector is actually boolean.
As stated by the README, the intention is for the shaders to be
provided under the terms of the Unlicense in addition to the MIT
and Apache-2.0 licenses.
While here, add a self-contained UNLICENSE file to replace the
external reference to unlicense.org.
