add support for argument to x, to enable removing (not-current) directory

[ahamid]

Workaround for #159

Does not work (PROMPT_COMMAND always adds $PWD again):
[user@there]$ z -x

Does work:
[user@here]$ z -x there

[ericbn]

As I understand (see #208 (comment)), the -x is already intended to be used with a regexp

$ z -x foo

meaning remove the current directory from the datafile, AND change to the directory matching foo. This is useful right after z foo when that is changing to a directory you don't want to go anymore.

See b9afd5f

[ahamid]

I have encountered this situation again, and z -x <previous-criteria> still does nothing for me

$ z -x foo

In fact, after running this many times ("until you land at target"), looks like it just keeps increasing the bad (current) directory's score. :(

[/base/foo/nested/wrong-foo]$ z -x foo
68         /base/foo
100        /base/foo/nested/wrong-foo
[/base/foo/nested/wrong-foo]$ z -x foo
68         /base/foo
104        /base/foo/nested/wrong-foo
[/base/foo/nested/wrong-foo]$ z -x foo
68         /base/foo
108        /base/foo/nested/wrong-foo
...

[tcely]

My work-around for this issue has been to cd to the directory I want gone, then use (_z -x; cd -) so that I'm no longer in the removed directory when my prompt command is run the next time.