Merge pull request #159 from Shougo/filter

Use core filter window feature

Add inputOptsFunc

Add previewContext in OnPreviewArguments

Fix actionParams

Use ddu.vim version 6

Remove pre version

Add exprParams

Only highlight items of "maxHighlightItems" to improve the performance.

feat:! "startAutoAction" is required if you want to enable autoAction…

… when UI initialized.

Fix