Fix CMake for SIMPLEXpress

Summary:
Build type and cpp14 to cpp17

Add SIMPLEXpress directory to config

fix config

Fix output directory error, add support for Apple, formatting in BUILDING.md

Pawlib working

Test Plan: rinkydink test code in main.cpp

Reviewers: jcmcdonald, wdede

Reviewed By: wdede

Subscribers: wdede, jcmcdonald

Tags: Programming [Dept], Ratscript [Project]

Maniphest Tasks: T1435

Differential Revision: https://phabricator.mousepawmedia.net/D375