v0.9.1

Feature:

• Support preview scroll offset relative to window height

  git grep --line-number '' |
    sk --delimiter : \
        --preview 'bat --style=numbers --color=always --highlight-line {2} {1}' \
        --preview-window +{2}-/2

Fix:

• #356 panic on ANSI enabled.
• tiebreak would now include score in the front of criterion if not specified.
• Reduce preview window flicking when moving cursor fast.
• Multiple preview window options weren't merged.
• pre-select-items should not contain empty string by default.
• click/wheel events's row weren't correct if --height is specified.