avutil: rename the string module

sys/src/avutil/bprint.rs

@@ -1,5 +1,5 @@
 use libc::{c_void, c_char, c_uchar, c_uint, c_int};
-use super::avstring::AVEscapeMode;
+use super::string::AVEscapeMode;
 
 #[repr(C)]
 pub struct AVBPrint {

sys/src/avutil/mod.rs

@@ -10,9 +10,9 @@ pub use self::aes::*;
 mod audio_fifo;
 pub use self::audio_fifo::*;
 
-mod avstring;
-pub use self::avstring::*;
-pub use self::avstring::AVEscapeMode::*;
+mod string;
+pub use self::string::*;
+pub use self::string::AVEscapeMode::*;
 
 mod base64;
 pub use self::base64::*;