[安装] MinGW雨威

This branch of MinGW installer contains several improvements in comparison with official version 5.1.4. It downloads and installs the same set of packages distributed from main MinGW SourceForge mirror. Changes from version MinGW-[RF]-5.1.6: * option to add MinGWin to PATH * /offline command line option for installer to skip checking for updates * automatically update version in license file * propose to inspect MinGW installation dir on uninstall only if it is not empty Changes from version MinGW-5.1.4: * fix numerical package version compare (previously 0.12 was < 0.9) * advanced uninstall log allows to remove only installed files * support for tar.bz2 and tar.lzma formats (no 7z, because compile/pack/unpack/NSIS toolchain is incomplete) * updated NSIS and plugins