Configure proper maximum width for rustfmt

* Changes:

- Add .rustfmt.toml.
- Specify max line width at 120 characters.

* Motivation:

100 is a wee bit too small, as evidenced by the changes in formatting.

.rustfmt.toml

@@ -0,0 +1 @@
+max_width = 120

src/interface.rs

@@ -222,9 +222,7 @@ where
         //      pre-conditions of `grow`.
         //  -   `new_ptr` is valid for `old_layout.size()` bytes, as `new_layout.size()` is greater than or equal to
         //      that as per the pre-conditions of `grow`.
-        unsafe {
-            ptr::copy_nonoverlapping(current_ptr.as_ptr(), new_ptr.as_ptr(), old_layout.size())
-        };
+        unsafe { ptr::copy_nonoverlapping(current_ptr.as_ptr(), new_ptr.as_ptr(), old_layout.size()) };
 
         //  Safety:
         //  -   `handle` has been allocated by `self`, as per the pre-conditions of `grow`.
@@ -266,9 +264,7 @@ where
         //  -   `new_ptr` is valid `new_layout.size()` bytes, as it was allocated with `new_layout`.
         //  -   `current_ptr` is valid for `new_layout.size()` bytes, as it is smaller than or equal to
         //      `old_layout.size()` as per the pre-conditions of `shrink`.
-        unsafe {
-            ptr::copy_nonoverlapping(current_ptr.as_ptr(), new_ptr.as_ptr(), new_layout.size())
-        };
+        unsafe { ptr::copy_nonoverlapping(current_ptr.as_ptr(), new_ptr.as_ptr(), new_layout.size()) };
 
         //  Safety:
         //  -   `handle` has been allocated by `self`, as per the pre-conditions of `shrink`.
@@ -311,9 +307,7 @@ where
         //      pre-conditions of `grow`.
         //  -   `new_ptr` is valid for `old_layout.size()` bytes, as `new_layout.size()` is greater than or equal to
         //      that as per the pre-conditions of `grow`.
-        unsafe {
-            ptr::copy_nonoverlapping(current_ptr.as_ptr(), new_ptr.as_ptr(), old_layout.size())
-        };
+        unsafe { ptr::copy_nonoverlapping(current_ptr.as_ptr(), new_ptr.as_ptr(), old_layout.size()) };
 
         //  Safety:
         //  -   `handle` has been allocated by `self`, as per the pre-conditions of `grow`.

src/lib.rs

@@ -10,6 +10,8 @@
 #![cfg_attr(not(test), no_std)]
 //  Features
 #![feature(allocator_api)]
+#![feature(maybe_uninit_write_slice)]
+#![feature(ptr_as_uninit)]
 #![feature(ptr_metadata)]
 #![feature(slice_ptr_get)]
 #![feature(specialization)]

src/storage/allocator_storage.rs

@@ -76,9 +76,7 @@ where
     }
 
     fn allocate_zeroed(&self, layout: Layout) -> Result<Self::Handle, AllocError> {
-        self.0
-            .allocate_zeroed(layout)
-            .map(|slice| slice.as_non_null_ptr())
+        self.0.allocate_zeroed(layout).map(|slice| slice.as_non_null_ptr())
     }
 
     unsafe fn grow_zeroed(