Ticks rendered after grid, previously it was the other way around, obvious since inside ticks have been introduced.
last_coord set to NULL during onLoad, originally it was set to coord_tern(), which was necessary for the default theme elements, however,
  is presumptuous in terms of what te user will actually plot.
tern_stop() function created.
set_last_coord introduced inside plot cosntruction function
tern_stop error handling for some convenience functions
Length of theme elements in 'units', such as major and minor ticks.
Correction of padding by aspect ratio, which was introducing small errrors in ticks, noticiable for long tick sizes.
Restructured cood_tern() and how it renderd the ternary elements, distinct functions were broken off from the main render_bg routine.