added ability to group rows of cells.
added setting for worksheet to set outline icon to top of row list.
fixed bug where wrong border style was being applied to merged cells
fixed bug that would cause excel4node to crash if undefined value was passed to cell
updated sample
Merge branch 'master' into dev

Conflicts:
	lib/Row.js
Merge branch 'master' into dev

Conflicts:
	lib/Row.js
	sample.js
bug tracking for group rows not expanding on first sheet.
invalid child when cells are grouped. possibly order?
fixed issue where scroll would not work properly when freezing both a row and a column
added ability to specify colors in multiple formats and still have OOXML validator validate results
experimental support for Grouping cells