Move mixer module to the sdl2-sys crate

The 'mixer' feature is re-exported so compiling without it will leave
out the mixer function definitions in sdl2-sys crate as well.
Progresses on Rust-SDL2#647

Author: jonemil

Cargo.toml

@@ -40,7 +40,7 @@ default = []
 ttf = []
 image = []
 gfx = ["c_vec"]
-mixer = []
+mixer = ["sdl2-sys/mixer"]
 
 use-bindgen = ["sdl2-sys/use-bindgen"]
 use-pkgconfig = ["sdl2-sys/use-pkgconfig"]

sdl2-sys/Cargo.toml

@@ -50,3 +50,4 @@ use-bindgen = ["bindgen"]
 static-link = []
 use_mac_framework = []
 bundled = ["cmake", "reqwest", "tar", "flate2"]
+mixer = []

sdl2-sys/src/lib.rs

@@ -9,3 +9,6 @@
 #![allow(non_snake_case)]
 
 include!(concat!(env!("OUT_DIR"), "/bindings.rs"));
+
+#[cfg(feature = "mixer")]
+pub mod mixer;

src/sdl2/mixer/ffi.rs renamed to sdl2-sys/src/mixer.rs

@@ -1,5 +1,4 @@
 use std::os::raw::{c_uint, c_int, c_char, c_double, c_void};
-use sys;
 
 pub type MIX_InitFlags = c_uint;
 pub const MIX_INIT_FLAC: c_uint = 1;
@@ -42,7 +41,7 @@ pub type Mix_EffectDone_t = ::std::option::Option<extern "C" fn(arg1: c_int,
                                                                   arg2: *const c_void)
                                                                  >;
 extern "C" {
-    pub fn Mix_Linked_Version() -> *const sys::SDL_version;
+    pub fn Mix_Linked_Version() -> *const ::SDL_version;
     pub fn Mix_Init(flags: c_int) -> c_int;
     pub fn Mix_Quit();
     pub fn Mix_OpenAudio(frequency: c_int,
@@ -55,10 +54,10 @@ extern "C" {
                          format: *mut u16,
                          channels: *mut c_int)
                          -> c_int;
-    pub fn Mix_LoadWAV_RW(src: *mut sys::SDL_RWops, freesrc: c_int) -> *mut Mix_Chunk;
+    pub fn Mix_LoadWAV_RW(src: *mut ::SDL_RWops, freesrc: c_int) -> *mut Mix_Chunk;
     pub fn Mix_LoadMUS(file: *const c_char) -> *mut Mix_Music;
-    pub fn Mix_LoadMUS_RW(src: *mut sys::SDL_RWops, freesrc: c_int) -> *mut Mix_Music;
-    pub fn Mix_LoadMUSType_RW(src: *mut sys::SDL_RWops,
+    pub fn Mix_LoadMUS_RW(src: *mut ::SDL_RWops, freesrc: c_int) -> *mut Mix_Music;
+    pub fn Mix_LoadMUSType_RW(src: *mut ::SDL_RWops,
                               type_: Mix_MusicType,
                               freesrc: c_int)
                               -> *mut Mix_Music;