Explicitly define PDC_WIDE constant

To enable wide-functions in PDCurses.
Support cross-building in Makefile.win
Use forward slashes in vifm.rc file
Add patches for PDCurses
Add instructions on building with MXE
Merge branch 'win-build-using-mxe'
Display better error message on app run failure
Document better error message on app startup fail
Merge branch 'win-better-exec-error-msg'