eulerr 1.1.0

Major changes

• eulerr() and its related methods been deprecated and are being replaced by
  euler(), which takes slightly different input. Notably, the default is
  now to provide input in the form of disjoint class combinations, rather
  than unions. This is partly to make the function a drop-in replacement for
  venneuler::venneuler.
• plot.euler() has been completely revamped, now interfacing xyplot() from
  lattice. As a result, arguments polygon_args, mar, and text_args have been
  deprecated.

Minor changes

• Added a counts argument to plot.eulerr, which intersections and
  complements with counts from the original set specificiation (#6).
• Added a key argument to plot.eulerr that prints a legend next to the
  diagram.
• Switched to atan2() from RcppArmadillo.
• Added version requirement for RcppArmadillo.
• Dropped dependency on MASS for computing label placement, replacing it
  with a faster, geometric algorithm.
• Dropped the cost function argument cost and now forces the function to
  use sums of squares, which is more or less equivalent to the cost function
  from venneuler.
• Color palettes in plot.euler() now chooses colors adapted to color vision
  deficiency (deuteranopia). With increasingly large numbers of sets, this
  adaptation is relaxed to make sure that colors are kept visually distinct.
• euler() now uses nlm() instead of optim(method = "Nelder-Mead") for
  its final optimization.

Bug fixes

• The previous algorithm incorrectly computed loss from unions of sets. It now
  computes loss from disjoint class combinations.
• Added missing row breaks in print.eulerr.