eulerr 2.0.0

Major changes

• eulerr() has been replaced with euler() (see update 1.1.0) and made
  defunct.
• There are two new methods for euler:
  • euler.list() produces diagrams from a list of sample spaces.
  • euler.table() produces diagrams from a table object, as long as there
    are no dimensions with values greater than 2.
• plot.euler() has been rewritten (again) from the ground up to better match
  other high-level functions from lattice. This change is intended to be
  as smooth as possible and should not make much of a difference to most users.
• Arguments polygon_args, mar, and text_args to plot.euler() have been
  made defunct.

Minor changes

• plot.euler() handles conflicting arguments better.
• c++ routines in eulerr now use registration.
• euler() now allows single sets (#9).
• Labels in plot.euler() now use a bold fontface by default in order to
  distinguish them from the typeface used for counts.
• Argument key in plot.euler() has been deprecated and replaced with
  auto.key. Notice that using key does not throw a warning since the
  argument is used in lattice::xyplot() (which plot.euler() relies on).
• Argument fill_opacity is softly deprecated and has been replaced with
  fill_alpha for consistency with other lattice functions.

Bug fixes

• border argument in plot.euler() works again (#7).