Updated tuple docujmentation for new functionality.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86782 b8fc166d-592f-0410-95f2-cb63ce0dd405
Corrected description.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86783 b8fc166d-592f-0410-95f2-cb63ce0dd405
Added left, right, center, justify items to cater for role text alignment as for color needed for PDF.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86784 b8fc166d-592f-0410-95f2-cb63ce0dd405