Update changelog and `@since` annotations

changelog.md

 ### 2.1.2
 
+* [Update case mappings for Unicode 16.0](https://github.com/haskell/text/pull/618)
+
 * [Add type synonym for lazy builders. Deprecated `StrictBuilder` for `StrictTextBuilder`](https://github.com/haskell/text/pull/581)
 
+* [Add `initsNE` and `tailsNE`](https://github.com/haskell/text/pull/558)
+
+* [Add `foldlM'`](https://github.com/haskell/text/pull/543)
+
+* [Add `Data.Text.Foreign.peekCString`](https://github.com/haskell/text/pull/599)
+
+* [Add `Data.Text.show` and `Data.Text.Lazy.show`](https://github.com/haskell/text/pull/608)
+
+* [Add pattern synonyms `Empty`, `(:<)`, and `(:>)`](https://github.com/haskell/text/pull/619)
+
+* [Improve precision of `Data.Text.Read.rational`](https://github.com/haskell/text/pull/565)
+
+* [`Data.Text.IO.Utf8`: use `B.putStrLn` instead of `B.putStr t >> B.putStr "\n"`](https://github.com/haskell/text/pull/579)
+
+* [`Data.Text.IO` and `Data.Text.Lazy.IO`: Make `putStrLn` more atomic with line or block buffering](https://github.com/haskell/text/pull/600)
+
+* [Integrate UTF-8 `hPutStr` to standard `hPutStr`](https://github.com/haskell/text/pull/589)
+
+* [Serialise `Text` without going through `ByteString`](https://github.com/haskell/text/pull/617)
+
+* [Make `splitAt` strict in its first argument, even if input is empty](https://github.com/haskell/text/pull/575)
+
+* [Improve lazy performance of `Data.Text.Lazy.inits`](https://github.com/haskell/text/pull/572)
+
+* [Implement `Data.Text.unpack` and `Data.Text.toTitle` directly, without streaming](https://github.com/haskell/text/pull/611)
+
+* [Make `fromString` `INLINEABLE` instead of `INLINE`](https://github.com/haskell/text/pull/571) to reduce the size of generated code.
+
 ### 2.1.1
 
 * Add pure Haskell implementations as an alternative to C-based ones,

src/Data/Text.hs

@@ -1041,6 +1041,8 @@ foldl1' f t = S.foldl1' f (stream t)
 {-# INLINE foldl1' #-}
 
 -- | /O(n)/ A monadic version of 'foldl''.
+--
+-- @since 2.1.2
 foldlM' :: Monad m => (a -> Char -> m a) -> a -> Text -> m a
 foldlM' f z t = S.foldlM' f z (stream t)
 {-# INLINE foldlM' #-}
@@ -2096,6 +2098,8 @@ overflowError :: HasCallStack => String -> a
 overflowError fun = P.error $ "Data.Text." ++ fun ++ ": size overflow"
 
 -- | Convert a value to 'Text'.
+--
+-- @since 2.1.2
 show :: Show a => a -> Text
 show = pack . P.show
 

src/Data/Text/Internal/Lazy.hs

@@ -51,6 +51,8 @@ import qualified Data.Text as T
 
 data Text = Empty
           -- ^ Empty text.
+          --
+          -- @since 2.1.2
           | Chunk {-# UNPACK #-} !T.Text Text
           -- ^ Chunks must be non-empty, this invariant is not checked.
             deriving (Typeable)

src/Data/Text/Lazy.hs

@@ -853,6 +853,7 @@ foldl1' f t = S.foldl1' f (stream t)
 
 -- | /O(n)/ A monadic version of 'foldl''.
 --
+-- @since 2.1.2
 foldlM' :: Monad m => (a -> Char -> m a) -> a -> Text -> m a
 foldlM' f z t = S.foldlM' f z (stream t)
 {-# INLINE foldlM' #-}
@@ -1828,6 +1829,8 @@ zipWith f t1 t2 = unstream (S.zipWith g (stream t1) (stream t2))
 {-# INLINE [0] zipWith #-}
 
 -- | Convert a value to lazy 'Text'.
+--
+-- @since 2.1.2
 show :: Show a => a -> Text
 show = pack . P.show