Changelog for copilot-theorem-3.3

2021-05-07 * Version bump (3.3). (#217). * Adjust contraints on version of what4. (#90). 2021-03-07 * Version bump (3.2.1). (#92). * Completed the documentation. (#95, #93). 2020-12-06 * Version bump (3.2). * Update description, bug-reports and homepage field in cabal file (#97). 2019-11-22 Ivan Perez <ivan.perez@nianet.org> * Version bump (3.1). * Remove ExternFun (#99).