improvement: update macros to not require manual imports

[timokoesters]

This should make it easier for users of the library, because they don't have to add random use statements for all the things the macros need.

[timokoesters]

It could be made even more robust by adding the absolute path for Vec and Ok, but I think that's too messy to read and has little benefit

[schungx]

My question is: what if the user pulls in Rhai under a different name?

[schungx]

There are some CI tests not passing. Can you also take care of those? Thanks.

[schungx]

Can you put in an attribute (e.g. root or crate_name) which defaults to rhai?

The test output failure I can fix.

[timokoesters]

I've implemented the root argument and added a test for it called one_arg_fn_with_context_custom_root

[schungx]

That test failure is strange. I'm looking into it, because I cannot reproduce it on my desktop, nor in my dev repo.

[schungx]

Should we add some tests with #[derive(CustomType(root="rhai"))] and #[export_module(root="rhai")] just to test out the attribute?

I'll also update the Book to mention this attribute and remove the need to import.

[timokoesters]

Small correction, the syntax is
#[derive(CustomType)]
#[rhai_type(root=oldrhai)]
struct MyCustomType {
}
I think more test would be useful. But you can rename rhai to something else, like use rhai as oldrhai.

Do you want me to add one derive test and one export_module test?