Wrapped long lines.
Some colspan fixes and improvements:
1. Added TableLayout.colspan(elem, colspan) for easy constraint configuration.
2. Documented TableLayout.Colspan class.
3. Fixed code in computeMetrics which used 1 for the colspan of every element
instead of the actual colspan. This caused crashes because the row count was
incorrectly computed and also caused layout errors because the row heights and
other bits were incorrectly computed. How this ever worked on any table
containing a >1 colspan element, I know not.