Avoid using extern crate when not needed

Rust 2018 allows to skip importing external crates using
`extern crate` expression in most of cases so update the code and examples
to take advantage of it.
`log` crate is imported the old way for now to avoid importing every level
in every file using the `use` keyword.

Author: rafalh

README.md

@@ -28,10 +28,6 @@ Add this to your `Cargo.toml`:
     [dependencies]
     fatfs = "0.4"
 
-and this to your crate root:
-
-    extern crate fatfs;
-
 You can start using the `fatfs` library now:
 
     let img_file = File::open("fat.img")?;
@@ -43,7 +39,6 @@ You can start using the `fatfs` library now:
 Note: it is recommended to wrap the underlying file struct in a buffering/caching object like `BufStream` from
 `fscommon` crate. For example:
 
-    extern crate fscommon;
     let buf_stream = BufStream::new(img_file);
     let fs = fatfs::FileSystem::new(buf_stream, fatfs::FsOptions::new())?;
 

examples/cat.rs

@@ -1,6 +1,3 @@
-extern crate fatfs;
-extern crate fscommon;
-
 use std::env;
 use std::fs::File;
 use std::io::{self, prelude::*};

examples/ls.rs

@@ -1,7 +1,3 @@
-extern crate chrono;
-extern crate fatfs;
-extern crate fscommon;
-
 use std::env;
 use std::fs::File;
 use std::io;

examples/mkfatfs.rs

@@ -1,6 +1,3 @@
-extern crate fatfs;
-extern crate fscommon;
-
 use std::env;
 use std::fs;
 use std::io;

examples/partition.rs

@@ -1,6 +1,3 @@
-extern crate fatfs;
-extern crate fscommon;
-
 use std::{fs, io};
 
 use fatfs::{FileSystem, FsOptions};

examples/write.rs

@@ -1,6 +1,3 @@
-extern crate fatfs;
-extern crate fscommon;
-
 use std::fs::OpenOptions;
 use std::io::{self, prelude::*};
 

src/boot_sector.rs

@@ -801,8 +801,7 @@ pub(crate) fn format_boot_sector<E: IoError>(
 #[cfg(test)]
 mod tests {
     use super::*;
-    extern crate env_logger;
-    use crate::core::u32;
+    use core::u32;
 
     fn init() {
         let _ = env_logger::builder().is_test(true).try_init();

src/dir_entry.rs

@@ -6,6 +6,7 @@ use core::fmt;
 #[cfg(not(feature = "unicode"))]
 use core::iter;
 use core::str;
+use bitflags::bitflags;
 
 #[cfg(feature = "lfn")]
 use crate::dir::LfnBuffer;

src/lib.rs

@@ -10,20 +10,9 @@
 //! fatfs = "0.4"
 //! ```
 //!
-//! And this in your crate root:
-//!
-//! ```rust
-//! extern crate fatfs;
-//! ```
-//!
 //! # Examples
 //!
 //! ```rust
-//! // Declare external crates
-//! // Note: `fscommon` crate is used to speedup IO operations
-//! extern crate fatfs;
-//! extern crate fscommon;
-//!
 //! use std::io::prelude::*;
 //!
 //! fn main() -> std::io::Result<()> {
@@ -60,14 +49,9 @@
 #![warn(clippy::pedantic)]
 #![allow(clippy::module_name_repetitions, clippy::cast_possible_truncation)]
 
-#[macro_use]
-extern crate bitflags;
-
 #[macro_use]
 extern crate log;
 
-extern crate core;
-
 #[cfg(all(not(feature = "std"), feature = "alloc"))]
 extern crate alloc;
 

tests/format.rs

@@ -1,7 +1,3 @@
-extern crate env_logger;
-extern crate fatfs;
-extern crate fscommon;
-
 use std::io;
 use std::io::prelude::*;