Windows support

Fixed incorrect parsing of --stdlib in configure
Added Emacs detection to configure to avoid build error on systems lacking it
Fixed removal of jenga-merlin in make uninstall
Added support for Windows .exe extension
Fixed build system to work with mingw (symlinks not available)
Fixed Vim Python script to use Popen correctly under windows
Fixed Vim Python script to hide the ocamlmerlin terminal window (it's not perfect - sadly it displays and is then hidden)