refactoring of RS_DimAngular, fix LibreCAD#911 and LibreCAD#824/Libre… …CAD#896

returning to LC via Command+Tab won't always activate a subwindow Lib… …reCAD#821 LibreCAD#814

eliminated build error for gcc 5.4 LibreCAD@8bedeb5751ac0b3490b9d5395741 687fc774eae9

ensured that draft mode is set for new drawings; LibreCAD#749 

set LC_VERSION="2.2.0-alpha" 

set LC_VERSION="2.1.0" 

added device options; LibreCAD#658 

switched version to 2.1.0-beta 

ellipse: fixed trim by amount(lengthen) 

updated README