Add is_account_empty as experimental method

Mv isAccountEmpty to experimental namespace

Add experimental as a cargo feature

Make experimental native methods private

src/experimental.rs

@@ -0,0 +1,18 @@
+//! Experimental methods.
+
+use super::*;
+
+mod native {
+    extern "C" {
+        pub fn experimental_isAccountEmpty(addressOffset: *const u32) -> u32;
+    }
+}
+
+pub fn is_account_empty(address: &Address) -> bool {
+    let ret = unsafe { native::experimental_isAccountEmpty(address.bytes.as_ptr() as *const u32) };
+    if ret != 0 && ret != 1 {
+        panic!();
+    }
+
+    ret == 1
+}

src/lib.rs

@@ -37,6 +37,9 @@ pub mod bignum;
 #[cfg(not(feature = "std"))]
 pub mod convert;
 
+#[cfg(feature = "experimental")]
+pub mod experimental;
+
 #[cfg(feature = "std")]
 use std::vec::Vec;