option to only search current line for closing pair

This adds the `g:AutoPairsMultilineClose` option.

    Default : 1

    When you press the key for the closing pair (e.g. `)`) it jumps past it.
    If set to 1, then it'll jump to the next line, if there is only whitespace.
    If set to 0, then it'll only jump to a closing pair on the same line.