Implement drawing a flag

[ErdaradunGaztea]

By default the flag should contain n strips of equal width with colors in order, but some flags work differently. For example, the transgender flag has symmetrical stripes. These flags should have custom plotting functions.

[ErdaradunGaztea]

Return a structure instead and implement a plotting function for it. The structure should consist of a vector of colors, sometimes duplicated (as in the case of trans flag, for example). Then there should be an attribute that describes the shape. Perhaps a function that translates this shape to a ggplot2 call, but not an attribute.