async: Add conversions from static slices to Body

These useful conversions were missed in #159.

refs #158

src/async_impl/body.rs

@@ -51,6 +51,13 @@ impl From<Vec<u8>> for Body {
     }
 }
 
+impl From<&'static [u8]> for Body {
+    #[inline]
+    fn from(s: &'static [u8]) -> Body {
+        reusable(Bytes::from_static(s))
+    }
+}
+
 impl From<String> for Body {
     #[inline]
     fn from(s: String) -> Body {
@@ -58,6 +65,13 @@ impl From<String> for Body {
     }
 }
 
+impl From<&'static str> for Body {
+    #[inline]
+    fn from(s: &'static str) -> Body {
+        s.as_bytes().into()
+    }
+}
+
 /// A chunk of bytes for a `Body`.
 ///
 /// A `Chunk` can be treated like `&[u8]`.