Implement vertical tab stops

Currently vertical tab stops are assumed to be present on every line. The ECMA-48 command for 

- 8.3.162 VTS - LINE TABULATION SET

is not implemented.

Consider implementing a vertical stop. The issue however is that the default behavior of a vertical tab is to treat every line as a vertical tab stop. However there doesn't seem to be a correlating code that clears the vertical tab stops.