short term trend application

[andybeet]

ggplot geom for short term trend

• Modified the GEOM related functions GeomLM, geom_lm, StatLM to allow for fitting of short term trend. (This calls arfit package, added to DESCRIPTION file)
• Changed the colors of the short term trend lines to be a darker color, made line solid
• Only calculates a trend if n >4

Plot function example

Modified the plot_gsi function to take an argument n, specifying the number of data points to use in the trend estimation. It defaults to n=0 to ensure backward compatibility (no trend estimated)

To view changes type: ecodata::plot_gsi(n=10) or ecodata::plot_gsi(n=20)

We can make any modifications to the appearance of the trend line, change color, thickness, style etc.