Auto remove bookmark after jump to it.

add option `bm-auto-remove-after-jump' variable

add param remove-after-jump-p to function `bm-bookmark-add'
  (defun bm-bookmark-add (&optional annotation time remove-after-jump-p)

I write a function name goto-definition, I want use bm.el to set a marker before goto-definition 
so I can jump back use bm ,but I want to auto remove the bookmark after jump back 
so I open this pull request.
```
(defun goto-definition (&optional arg)
  "Make use of emacs' find-func and etags possibilities for finding definitions."
  (interactive "P")
    (bm-bookmark-add line nil t)
     ....
     ;; do something ...
```
This method is only used inside (bm-goto ...) so the logic should be moved there. Then the logic can be alot simpler as well.