Add CMake support for less

[red-rj]

For CMake 3.8 and up, as an alternative for autoconf or the Windows makefile.

• defines.cmake.in is configured by CMake into defines.h.
• user preferences can be controlled via CMake cmd. line or CMakeCache.txt.
• handles dependency checking and defines HAVE_ macros* like autoconf, but only those that affect less.

*Note: macros for stuff defined in the C standard, like HAVE_ANSI_PROTOS, HAVE_CONST, HAVE_STDLIB_H, are hard-coded to 1 in defines.cmake.in. I assume most people using CMake aren't also using an ancient compiler.

I tested it on windows 10 and linux mint.

Other improvements:

• [Windows] use USERPROFILE as HOME, if not defined.
• [Windows] fixed a crash on use_logfile, due to bad permission bits.
• [Windows] use ReplaceFileA on save_cmdhist, atomically replaces lesshist and preserves file attributes.
• add EDIT_PROTO config, controls the default editor prompt if LESSEDIT is not set.
• add HAVE_LANGINFO check for langinfo.h.