* update build instruction for legacy Windows
* add CI build for windows legacy
* merge mingw CI builds
* merge deb CI builds
* fix typo
* bump qt 5.6 build
* improve Qt 5.6 support
* switch registry API to Windows XP compatible Unicode API
* update docs
* add comment for `CONFIG += c++14 c++17` in qmake .pro files
* fix logic for lockFile