Macro emacs::emacs_export_functions

macro_rules! emacs_export_functions {
    ($env:expr, $prefix:expr, $mappings:tt,) => { ... };
    ($env:expr, $prefix:expr, {
        $( $name:expr => $declaration:tt ),+,
    }) => { ... };
    ($env:expr, $prefix:expr, {
        $( $name:expr => $declaration:tt ),*
    }) => { ... };
    (decl, $env:expr, $prefix:expr, $name:expr, ($func:path, $( $opt:expr ),+,)) => { ... };
    (decl, $env:expr, $prefix:expr, $name:expr, ($func:path, $( $opt:expr ),+)) => { ... };
}

Export Rust functions so that Lisp code can call them by name.