Add replace-query action

replace-query action replaces the query string with the current
selection. If the selection is too long, it will be truncated.

If the line contains meta-characters of fzf search syntax, it is
possible that the line is no longer included in the updated result.

e.g.

  echo '!hello' | fzf --bind ctrl-v:replace-query

Close #1137

src/terminal.go

@@ -203,6 +203,7 @@ const (
 	actJump
 	actJumpAccept
 	actPrintQuery
+	actReplaceQuery
 	actToggleSort
 	actTogglePreview
 	actTogglePreviewWrap
@@ -1568,6 +1569,11 @@ func (t *Terminal) Loop() {
 				}
 			case actPrintQuery:
 				req(reqPrintQuery)
+			case actReplaceQuery:
+				if t.cy < t.merger.Length() {
+					t.input = t.merger.Get(t.cy).item.text.ToRunes()
+					t.cx = len(t.input)
+				}
 			case actAbort:
 				req(reqQuit)
 			case actDeleteChar: