Deprecate Value::as_str and Value::as_string_lossy

These methods don't follow Rust naming convention, see
https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv

src/string.rs

@@ -86,7 +86,7 @@ impl String {
 
     /// Get the bytes that make up this string.
     ///
-    /// The returned slice will not contain the terminating nul byte, but will contain any nul
+    /// The returned slice will not contain the terminating null byte, but will contain any null
     /// bytes embedded into the Lua string.
     ///
     /// # Examples
@@ -106,15 +106,15 @@ impl String {
         BorrowedBytes::from(self)
     }
 
-    /// Get the bytes that make up this string, including the trailing nul byte.
+    /// Get the bytes that make up this string, including the trailing null byte.
     pub fn as_bytes_with_nul(&self) -> BorrowedBytes<'_> {
         let BorrowedBytes { buf, borrow, _lua } = BorrowedBytes::from(self);
-        // Include the trailing nul byte (it's always present but excluded by default)
+        // Include the trailing null byte (it's always present but excluded by default)
         let buf = unsafe { slice::from_raw_parts((*buf).as_ptr(), (*buf).len() + 1) };
         BorrowedBytes { buf, borrow, _lua }
     }
 
-    // Does not return the terminating nul byte
+    // Does not return the terminating null byte
     unsafe fn to_slice(&self) -> (&[u8], Lua) {
         let lua = self.0.lua.upgrade();
         let slice = {