Add a new wren_lib static library project to the Visual Studio 2013 solution, moving all VM source files (wren_compiler.c, wren_core.c, wren_debug.c, wren_io.c, wren_utils.c, wren_value.c, wren_vm.c) from the wren executable project into the library. The wren project now only contains CLI-specific sources (main.c, io.c, vm.c) and links against wren_static_d.lib. Update .gitignore to exclude Debug/ and Release/ build output directories.
Add MSVC 2013 project scaffolding under project/msvc2013/ including wren.sln solution file, wren.vcxproj with Debug/Release Win32 configurations using v120 toolset, and wren.vcxproj.filters organizing source and header files from ../src/ into Visual Studio filter categories.
