Macros are not self-contained

[nyurik]

Exported Rust macros (per best "hygiene" practices) should not require any external paths to be brought into local scope. So, if a crate exports a macro, that macro should only use fully-qualified items from the same crate, or more specifically - use the $crate metavariable per docs.

At least declare_stack_allocator_struct! macro uses non-fully-qualified identifiers like declare_stack_allocator_struct! inside, requiring crate users to use it, making the code unclean and possibly error prone.

[danielrh]

Can you put up a PR to do this?