initial POC pander theme
add support for disabling grid(s)
add support for grid line type
add support for suppressing (or tweaking) margin around the plot
add support for font family/color/size
panel and plot background, box around plot, small fixes in docs and
ticks color
add support for legend position
add support for axis angle
add color palette
fix: typo in calc theme demo
add theme_pander related stuff
update examples for theme_pander and fix typo in the Calc theme