transparency and shading; change wrt verbatimtex

Merge pull request #14 from dohyunkim/master

v2.2

v2.1: Merge pull request #9 from dohyunkim/master

support 'withcolor' option

v2.03: Merge pull request #8 from dohyunkim/master

using textext() or TEX(), labels can be typeset with variables