maplegend_0.4.0

fix

Most of the functions of the package have been refactored in order to use a more
robust behaviour and to be suitable for plots with asp != 1.

feat

• new map type "histo" to draw hitogram legends (#5)
• new args val_big and val_dec have been added for types already using val_rnd
  to select decimal separator and big values separator (#6)