Changing continent's color in PlotEquiMap()

This issue introduces two new options to PlotEquiMap():

1. 'col.borders' allows the user to set the color of the border of the continents (instead of the standard black) and
2. 'col.lakes' set the color of the lakes and seas inside continents (i.e: Black Sea, Caspian Sea), which is white by default. This second option works only when filled.continents = TRUE. Notice that the inner color of the continents (gray) when filled.continents = TRUE cannot be modified by these options.