Added OS abstraction for directory listing in replay.c. (credits to @segrax for his work in #118, I could base the Win32 code on his code!)
Other minor code fixes, to make the source code play well with the MSVC compiler.
Added build.bat for compiling from the command-line, using the MSVC toolset. Added explanation in doc/Readme.txt.
Updated NMakeFile (added lighting.obj and screenshot.obj; output prince.exe to the base dir; tweaked the compiler options a bit)
Removed unistd_win.h, because it does not seem to be needed (and, incidentally, in common.h, including unistd.h also doesn't appear to be necessary...)
CMakeLists.txt: Prevent Visual Studio from running CMake (one should use build.bat or NMake instead)
CMakeLists.txt: For SDL2 include and lib directories, automatically pick the right architecture (x86 or x64), so you don't need to manually specify the architecture-specific subdirectories from the SDL2 download package.
Changes: