We enable symlink support using the --links command line switch.
When symlink support is enabled, the mount backends will translate
the name of the vfs symlinks files (truncating their rclonelink suffix).
Also, operations like rename, symlink etc does not needs the rclonelink
suffix, it is handled internally to pass it to the underlying low level
VFS.
When symlink support is disabled, Symlink and Readlink functions will
transparently manage ".rclonelink" files as regular files.
Fixes#2975
This is possible now that we no longer support go1.12 and brings
rclone into line with standard practices in the Go world.
This also removes errors.New and errors.Errorf from lib/errors and
prefers the stdlib errors package over lib/errors.
