Add `/Since:/` Haddock annotations

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
`M-x delete-trailing-whitespace` & `M-x untabify`

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Convert `deepseq.cabal` to `cabal-version>=1.10`

This also resurrects compatibility with older GHC versions back to
version 7.0.1 and specifies more accurate and verified build-depends.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>