Changelog for glpk-headers

[Unreleased]

• The mkHaskellErrorHook function was added to Math.Programming.Glpk.Headers to support writing GLPK error handlers.

• The mkHaskellTermHook function was added to Math.Programming.Glpk.Headers to support writing GLPK terminal callback hooks.

• The mkHaskellMIPCallback function was added to Math.Programming.Glpk.Headers to support writing MIP callback functions.

[0.5.0] -- 2021-03-07

• Switch from Stack to Cabal (and Nix).
• Update to GHC 8.8.4