Fix and improve cairomm NMake Makefiles (cairomm-1-14 branch)

Hi,

This attempts to update the NMake Makefiles in the cairomm-1-14 branch by:

• Fix builds from release tarballs, to not generate cairomm.rc and cairommconfig.h when they already exist. This also fixes the process so that when we need to generate these files, it will be done automatically when running the all target, and ensures that the needed version info is indeed included.

• Make the USE_MESON_LIBS option to build DLLs and .lib's with Meson-style naming, so that we can distinguish between builds that use this option and builds that do not use this option (and the same with pangomm and gtkmm builds, that will make use of cairomm)

• Use the /utf-8 compiler flag when on Visual Studio 2015 or later.

• Update .gitignore that we do not track files under MSVC_NMake/ that are generating files during the build

With blessings, thank you!