Migrate crates to Rust edition 2021 (#24)

* Migrate ffmpeg-sys to Edition 2021

* Migrate ffmpeg to Edition 2021

* Remove now-redundant imports

* Reorder imports after edition migration

src/filter/context/context.rs

@@ -1,9 +1,9 @@
 use std::marker::PhantomData;
 
 use super::{Sink, Source};
-use ffi::*;
+use crate::ffi::*;
+use crate::{format, option, ChannelLayout};
 use libc::c_void;
-use {format, option, ChannelLayout};
 
 pub struct Context<'a> {
     ptr: *mut AVFilterContext,

src/filter/context/sink.rs

@@ -1,7 +1,7 @@
 use super::Context;
-use ffi::*;
+use crate::ffi::*;
+use crate::{Error, Frame};
 use libc::c_int;
-use {Error, Frame};
 
 pub struct Sink<'a> {
     ctx: &'a mut Context<'a>,

src/filter/context/source.rs

@@ -1,8 +1,8 @@
 use std::ptr;
 
 use super::Context;
-use ffi::*;
-use {Error, Frame};
+use crate::ffi::*;
+use crate::{Error, Frame};
 
 pub struct Source<'a> {
     ctx: &'a mut Context<'a>,

src/filter/filter.rs

@@ -3,7 +3,7 @@ use std::marker::PhantomData;
 use std::str::from_utf8_unchecked;
 
 use super::{Flags, Pad};
-use ffi::*;
+use crate::ffi::*;
 
 pub struct Filter {
     ptr: *mut AVFilter,

src/filter/flag.rs

@@ -1,4 +1,4 @@
-use ffi::*;
+use crate::ffi::*;
 use libc::c_int;
 
 bitflags! {

src/filter/graph.rs

@@ -3,9 +3,9 @@ use std::ptr;
 use std::str::from_utf8_unchecked;
 
 use super::{Context, Filter};
-use ffi::*;
+use crate::ffi::*;
+use crate::Error;
 use libc::c_int;
-use Error;
 
 pub struct Graph {
     ptr: *mut AVFilterGraph,

src/filter/mod.rs

@@ -16,9 +16,9 @@ pub use self::graph::Graph;
 use std::ffi::{CStr, CString};
 use std::str::from_utf8_unchecked;
 
-use ffi::*;
+use crate::ffi::*;
 #[cfg(not(feature = "ffmpeg_5_0"))]
-use Error;
+use crate::Error;
 
 #[cfg(not(feature = "ffmpeg_5_0"))]
 pub fn register_all() {

src/filter/pad.rs

@@ -2,8 +2,8 @@ use std::ffi::CStr;
 use std::marker::PhantomData;
 use std::str::from_utf8_unchecked;
 
-use ffi::*;
-use media;
+use crate::ffi::*;
+use crate::media;
 
 pub struct Pad<'a> {
     ptr: *const AVFilterPad,