Bump version & update changelog

Fix links in CHANGELOG

[skip ci]

Fix stack-lts-15.3.yaml filename

Fix changelog

Add missing entry to changelog

[skip ci]

Update to libsass 3.5.2 & bump version

Bump version [ci skip]

Fix README [ci skip]

Fix build process for Stack 1.4 & Cabal 1.24

Update changelog

[ci skip]