Add `#![deny(missing_docs)]` across multiple crates and fill in
documentation for all public items, including struct fields, enum
variants, trait methods, and proc macros.  Also mark two shell scripts
as executable.

Add `docs_rs` feature flag to enable docs.rs-specific configuration,
including `--generate-link-to-definition` and logo display.

Include the feature in build scripts, editor settings, and feature
constants for consistent documentation generation.

Update all documentation and code examples to use the new
`#[renderer(buffer)]`
pattern with `r_println!` instead of manually constructing
`RenderResult`
with `writeln!`.

macros

Reintroduce `r_print!` and `r_println!` macros as public exports, now
supporting both explicit buffer argument and implicit `#[buffer]` attr.
Add `#[buffer]` attribute macro that wraps unit-returning functions to
produce a `RenderResult` with an automatically injected buffer variable.
Relax `RenderResult::print()` and `println()` to accept `impl
AsRef<str>`.

Move routing methods exclusively to the `Routable` trait and update
all macro-generated code to reference `Routable` instead of `Grouped`

BREAKING CHANGE: Remove `mingling_support` feature from arg-picker
crate. The
`EntryPicker` trait and `corebind` module are now part of the mingling
crate
directly, and `build_pattern1` is now a public method.