r2dii.plot 0.4.0

Breaking changes

• All plot_*() functions have had the data preparation step extracted into
  prep_*() functions. This means that from now on prep_*() function needs to be called on data prior to plot_*(). The APIs of qplot_*() functions remain unchanged (#465).
• scale_colour_r2dii has argument renamed from labels to colour_labels (#527).

New features

• techmix plot does not show the start year scenario bar anymore. (#513)

Bug fixes

• scale_colour_r2dii, with input colours and levels, now outputs line plot with correctly coloured lines (#527).