impl PartialEq between Slice and []

```rust
impl<K: PartialEq, V: PartialEq> PartialEq<[(K, V)]> for map::Slice<K, V> {...}
impl<K: PartialEq, V: PartialEq> PartialEq<map::Slice<K, V>> for [(K, V)] {...}

impl<T: PartialEq> PartialEq<[T]> for set::Slice<T> {...}
impl<T: PartialEq> PartialEq<set::Slice<T>> for [T] {...}
```

Resolves #375

(cherry picked from commit cf9397f)

Author: cuviper

src/map/slice.rs

@@ -335,6 +335,22 @@ impl<K: PartialEq, V: PartialEq> PartialEq for Slice<K, V> {
     }
 }
 
+impl<K: PartialEq, V: PartialEq> PartialEq<[(K, V)]> for Slice<K, V> {
+    fn eq(&self, other: &[(K, V)]) -> bool {
+        self.len() == other.len() &&
+            // mapping from `&(K, V)` to `(&K, &V)`
+            self.iter().eq(other.iter().map(|(k, v)| (k, v)))
+    }
+}
+
+impl<K: PartialEq, V: PartialEq> PartialEq<Slice<K, V>> for [(K, V)] {
+    fn eq(&self, other: &Slice<K, V>) -> bool {
+        self.len() == other.len() &&
+            // mapping from `&(K, V)` to `(&K, &V)`
+            self.iter().map(|(k, v)| (k, v)).eq(other)
+    }
+}
+
 impl<K: Eq, V: Eq> Eq for Slice<K, V> {}
 
 impl<K: PartialOrd, V: PartialOrd> PartialOrd for Slice<K, V> {

src/set/slice.rs

@@ -225,6 +225,18 @@ impl<T: PartialEq> PartialEq for Slice<T> {
     }
 }
 
+impl<T: PartialEq> PartialEq<[T]> for Slice<T> {
+    fn eq(&self, other: &[T]) -> bool {
+        self.len() == other.len() && self.iter().eq(other)
+    }
+}
+
+impl<T: PartialEq> PartialEq<Slice<T>> for [T] {
+    fn eq(&self, other: &Slice<T>) -> bool {
+        self.len() == other.len() && self.iter().eq(other)
+    }
+}
+
 impl<T: Eq> Eq for Slice<T> {}
 
 impl<T: PartialOrd> PartialOrd for Slice<T> {