auto enlarge filtering range when enabling auto filter

Current Spec.

For standard usage, users should select the whole range of the data according to office doc.
Currently, keikai already supports
1. [standard usage] If users select a range, keikai set the user-selected range as the filtering range.
2. [smart guess] if users select 1 cell only, keikai auto detects adjacent non-empty cells to enlarge the filtering range.

Proposed new feature

Follow Excel spec.
1. When users select multiple cells in one row only, enlarge the filtering range to selected columns in the row. For example, a user selects A1:C1, keikai will search column A:C from row 1 for non-empty cells to create the filtering range.