Move app_io crate to the kernel/ (theseus-os#480)

Necessary for future usage by in-kernel WASM components, e.g., theseus-os#472

kernel/app_io/src/lib.rs

@@ -1,16 +1,17 @@
-//! This crate is an application-level library that stores the IO queues and pointers to terminal instances for running applications.
-//! It provides some APIs similar to std::io for applications to access those queues.
+//! A simple library that handles stdio queues for applications running in terminal instances.
+//! 
+//! This provides some APIs similar to Rust's `std::io` for applications to access those queues.
 //! 
 //! Usage example:
-//! 1. shell spawns a new app, and creates queues of `stdin`, `stdout` and `stderr`
-//! 2. shell stores the reader of `stdin` and writer of `stdout` and `stderr` to `app_io`,
-//!    along with the reader of key event queue and the pointer to the running terminal instance.
-//! 3. app calls app_io::stdin to get the reader of `stdin`, and can perform reading just like
+//! 1. shell spawns a new app, and creates queues of `stdin`, `stdout`, and `stderr` for that app.
+//! 2. shell stores the reader for `stdin` and writers for `stdout` and `stderr` to `app_io`,
+//!    along with the reader of the key events queue and references to the running terminal instance.
+//! 3. app calls [`stdin()`] to get the reader of `stdin`, and can perform reading just like
 //!    using the standard library
-//! 4. app calls app_io::stdout to get the writer of `stdin`, and can perform output just like
+//! 4. app calls [`stdout()`] to get the writer of `stdin`, and can perform output just like
 //!    using the standard library
-//! 5. after app exits, shell would set EOF flags to its `stdin`, `stdout` and `stderr` queues.
-//! 6. if all apps in a job exit, app shell removes all the structure stored in `app_io` and
+//! 5. after app exits, shell would set `EOF` flags to its `stdin`, `stdout`, and `stderr` queues.
+//! 6. once all apps in a job exit, app shell removes all the structure stored in `app_io` and
 //!    destructs all stdio queues
 
 #![no_std]

tlibc/Cargo.toml

@@ -25,7 +25,7 @@ path = "../kernel/memory"
 path = "../kernel/task"
 
 [dependencies.app_io]
-path = "../applications/app_io"
+path = "../kernel/app_io"
 
 
 ## Needed for building tlibc as a "staticlib" crate-type,