Update: added `RColorbrewer` to dependencies.
Update: expanded temporal range of GSOD built-in data to 1980-2000.
Update: added package `ggplot2` to dependencies.
Minor update: modified temporal range in example.
Major update: added documentation to `seasonalShift()`, implemented `Rsenal` check, implemented compatibility to `data.frame` objects, implemented visualization of parameters 'MIN' and 'MAX', disabled visualization of multiple start and end ranges in one plot.