initial VFS work

converted to an exception-based API for the FS/VFS

 - added symlink, follow_link, unlink, rmdir, stat, setattr and readdir support to VFS
 - added support for stat, lstat, fstat, fsync, lockf, symlink, readlink, chmod, fchmod, chown, fchown, chdir, fchdir, posix_fallocate, truncate, ftruncate, feof, ferror, fseek
 - removed inode.type property
 - support FS.ignorePermissions
 - added compatibility shims