herbstluftwm: update to 0.6.2
jdk7: update patchversion 51 -> 55.
Bump mpv to 0.3.8
Add subtitle option for ffmpeg.
Fix whitespace
Shea told me composableDerivation is hard to understand.

Thus comment it and why it was written long time ago until it'll get replaced piecewise.
Add expression for Haskell library 'these'
Add expression for the Agda standard library
haskell-hledger-irr: update to version 0.1.1.4
haskell-arithmoi: update to version 0.4.1.0
haskell-classy-prelude-conduit: update to version 0.9.1
haskell-classy-prelude: update to version 0.9.1
haskell-conduit-combinators: update to version 0.2.5.1
haskell-conduit-extra: update to version 1.1.0.3
haskell-conduit: update to version 1.1.1.1
haskell-hledger-lib: update to version 0.23
haskell-hledger-web: update to version 0.23
haskell-hledger: update to version 0.23
haskell-streaming-commons: update to version 0.1.2.1
curl: minor update 7.35.0 -> 7.36.0, including CVE fixes