A crate helping with structuring the library crate of a proc-macro package.
The major of this crate is macro proc_macro_api!,
which can export functions in submodules of a proc-macro crate as
the Application Programing Interfaces (APIs) of that proc-macro crate.
For example, assuming sub is a submodule of the root of
a proc-macro crate and has a function,
pub fn proc_fn(input: TokenStream) -> TokenStream, in order to export
proc_fn as a function-like macro, proc_macro_api! can be used in the
root of the crate like:
proc_macro_api!
Then, a function-like macro, proc_fn!(), is available from that
proc-macro crate.
Note: See the crate documentation for more details.