Highlight selected line in target window.

Also add a mark `l` for that line, so you can go back there with 'l .
use s:FocusCtrlsfWindow instead
Add option `g:ctrlsf_current_line_hl`, add command

`:CtrlSFClearHighlight`
Feature: highlight landing line after jumping

original author: unc0
modified by: dyng
Merge branch 'unc0-highlight' into future