* lib: Provide entrypoint through Ash loader w.o. implementing Entry
Ash recently [dropped all traits](1) to simplify `ash::Device` usage,
but this also disallows ash-molten from overriding the `EntryV1_0` trait
to provide a static entrypoint intead.
Fortunately ash-molten can simply pass a library loading closure that
returns the static address of `vkGetInstanceProcAddr` to
`EntryCustom::new_custom`, getting rid of the copied `fn
create_instance` implementation at the same time.
[1]: https://github.com/MaikKlein/ash/pull/412
* cargo: Disable unneeded `libloading` feature in Ash
The entry-point is statically linked from `MoltenVK` and does not need
any dlopen nor dlsym functionality.
* Fix some typos
