improve phrasing of CompressionScheme docs

src/compression_scheme.rs

@@ -10,14 +10,14 @@ pub trait CompressionScheme {
     /// Encode some bytes into `buf`, returning a [`Header`][Self::Header].
     ///
     /// This does not necessarily have to be deterministic,
-    /// but it **must** always be decodable by [`decode`](Self::decode).
+    /// but it **must** be decodable by [`decode`](Self::decode).
     /// That is, [`decode`](Self::decode) ∘ [`encode`](Self::encode) = `id`.
     fn encode(src: &[u8], buf: &mut BitVec) -> Self::Header;
 
     /// Decode the given bits and header into `buf`.
     ///
     /// This may panic on arbitrary input,
-    /// but it **must** always decode outputs of [`encode`](Self::encode).
+    /// but it **must** successfully decode outputs of [`encode`](Self::encode).
     /// That is, [`decode`](Self::decode) ∘ [`encode`](Self::encode) = `id`.
     fn decode(src: &BitSlice, header: &Self::Header, buf: &mut Vec<u8>);