Improve swiper for multiple occurrences on one line
* swiper.el (swiper--current-line):
(swiper--current-match-start): New defvar.
(swiper--init): Update.
(swiper--update-input-ivy): Don't move to line NUM if
`swiper--current-line' is equal to NUM. Later, store NUM in
`swiper--current-line' to avoid calling `line-number-at-pos'.
Additionally store `swiper--current-match-start' - it's necessary to
move there before searching for the regexp, since the point currently is
after the old regexp.