fixed #39: new function knit_child() to be used to output child documents in LaTeX
fixed #39: new function knit_child() to be used to output child documents in LaTeX

fboehm/labnotebook,fboehm/labnotebook,antass/labnotebook3,fboehm/cboettig_site,fboehm/labnotebook,fboehm/cboettig_site,fboehm/labnotebook,antass/labnotebook3,antass/labnotebook3,fboehm/labnotebook,fboehm/labnotebook,fboehm/cboettig_site,fboehm/cboettig_site,fboehm/cboettig_site