fixed issue #314

I assume that the documentation is wrong and that > should join with the next cell, the same way it's done in TWC.

But to comply with the ~ logic, I introduced < which will join with the cell to the left.

At the same time I fixed a bug with > at the end of a line. Usually it should be handled like "<", but it's ignoring an existing colspan. To illustrate, try this:

    |a|b|c|d|e|f|
    |A|B|>|>|E|>|
    |a|b|c|d|e|f|

for "E" you'll get a colspan of 2 instead of 4.