allowing the tltextend and tltextstart commands to have an additional optional argument for their anchor
fixing positioning of labels of new command, plus adding variables for startyear/endyear anchors and above/below values
when changing anchor or above/below values, append changes to the corresponding style
instead of appending to the startyear/endyear styles, overwrite the styles by adding two additional commands to update start or endyear styles, and having variables for anchor, above/below value and font for startyear and endyear.