format tags: option to crop from beginning of the string

[bart9h]

When using "%30@" for example, it would be more useful to show the end of the path, instead of cropping the end and showing only the beginning.

[gabime]

If its too long %s can be used to show only the basename.

[bart9h]

@gabime, that's what I'm doing now, but I wanted to show part of the path too.

Also, cropping from the beginning may be useful for other data besides the path.