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>`.

Remove the `Default` bound from `pick()` and `EntryPicker::pick()`,
allowing non-Default types to be used as arguments.

Add `IntoPicker::pick_or`, `pick_or_default`, and `pick_or_route`
convenience methods for common fallback patterns.

Fix token splitting in `arg!` macro to correctly handle angle brackets.

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

Move the REMAINS constant definition into arg_picker and re-export it
through mingling's constants module for unified access

methods

Deprecate `ShellContext` methods `filling_argument_first`,
`filling_argument`, `typing_argument`, `strip_typed_argument`, and
`get_typed_arguments` when the `picker` feature is active, as they
do not work under all `ParserStyle` settings.

Add `#![allow(deprecated)]` to the affected modules to suppress
warnings from internal usage.