Auto merge of rust-lang#263 - bluss:printf, r=alexcrichton

Add the family of printf, scanf functions

snprintf is apparently supported in MSVC since version 14. I'm curious to take the tests for a spin.

src/unix/mod.rs

@@ -179,6 +179,16 @@ cfg_if! {
 }
 
 extern {
+    pub fn fprintf(stream: *mut ::FILE,
+                   format: *const ::c_char, ...) -> ::c_int;
+    pub fn printf(format: *const ::c_char, ...) -> ::c_int;
+    pub fn snprintf(s: *mut ::c_char, n: ::size_t,
+                    format: *const ::c_char, ...) -> ::c_int;
+    pub fn sprintf(s: *mut ::c_char, format: *const ::c_char, ...) -> ::c_int;
+    pub fn fscanf(stream: *mut ::FILE, format: *const ::c_char, ...) -> ::c_int;
+    pub fn scanf(format: *const ::c_char, ...) -> ::c_int;
+    pub fn sscanf(s: *const ::c_char, format: *const ::c_char, ...) -> ::c_int;
+
     #[cfg_attr(target_os = "netbsd", link_name = "__socket30")]
     pub fn socket(domain: ::c_int, ty: ::c_int, protocol: ::c_int) -> ::c_int;
     #[cfg_attr(all(target_os = "macos", target_arch = "x86"),