Removed autoconf-dependent files, rewritten with cmake scripts

Turn USE_MT_GENTILES on for compilation and log its use.

Also fix typo in INSTALL instructions.

Removed boost filesystem and Magick++, as passing std::string across library boundaries in a pain in the neck to port reliably to multiple architectures. Replaced the former with direct methods and the latter with the latest MagickWand API. Also added some comments bits for Windows MinGW report, which need refactoring into the main CMake script

Change required version to 3.15 (older Debian distros still use this)
Change requirement from Magick++-config to Magickwand-config (as the older C API is being used as it plays nicer with MinGW)