theme_timeline: Theme for the earthquake data
In wingtham/NOAA: Read, Cleanse and Visualise NOAA Dataset

A few tweaks to turn off the background and grids.

1	theme_timeline()

a theme object to be attached to ggplot command

## Not run: ggplot(data = selected) +
aes(x=DATE, y=COUNTRY,
   colour = TOTAL_DEATHS,
   size = EQ_PRIMARY) +
   geom_timeline(xmin=xmin, xmax=xmax) +
   theme_timeline() +
   scale_size_continuous(name = "Richter scale value") + #change legend name
   scale_colour_continuous(name = "# Deaths") +
   scale_x_date(limits = c(xmin-months(6), xmax+months(6))) #extend the axis
## End(Not run)