This fixes several problems with MSVC build and Windows:
Adds VS things to .gitignore
Fixes path processing not handling backslash separators
Fixes extract failure with absolute paths due to the directory existence check attempting to call stat on the drive, which doesn't work, then attempting to call _mkdir for the drive, which also doesn't work
Fixes libunshield not exporting any symbols in DLL configuration
This fixes several problems with MSVC build and Windows:
stat
on the drive, which doesn't work, then attempting to call_mkdir
for the drive, which also doesn't work