plot_rate_change: Plot rate of change
In WDNR-Water-Use/CSLSlevels: CSLS Lake Level Analysis

Given a data frame with lake levels for a single lake or multiple lakes, plot the typical rate of change over a given time interval. If data frame has multiple lakes, will display as facet plots.

plot_rate_change(
  df,
  lag_months = c(1, 3, 12),
  convert_to_ft = TRUE,
  show_zero = TRUE,
  show_median = TRUE,
  show_labels = TRUE,
  max_rate = NULL,
  title = "",
  text_size = 12,
  vline_color = "#c00000",
  hist_color = "grey80",
  density_color = "#c00000",
  line_size = 1,
  lakes = c("Pleasant", "Long", "Plainfield")
)

`df`	a data frame with columns for "lake", "date", "level_obs", and "level_pred" that matches desired time series to analyze
`lag_months`	number of months to analyze rise/fall over, defaults to 1
`convert_to_ft`	defaults to true to converet rates from m/time period to ft/time period
`show_zero`	logical defaults to TRUE to plot vertical line at median number of months.
`show_median`	logical defaults to TRUE to display median rise/fall rates
`show_labels`	logical defaults to TRUE to label median rise/fall rates (if displayed)
`max_rate`	default to NULL, otherwise used to set max x limits
`title`	string to use for title of plot, defaults to "".
`text_size`	size of text, defaults to 12
`vline_color`	color of vertical line, defaults to a red ("#c00000")
`hist_color`	color of histogram bins, defaults to "grey80"
`density_color`	color of density curve with alpha = 0.2, defaults to a red ("#c00000")
`line_size`	line size, defaults to 1
`lakes`	vector of lakes to include in plot. Defaults to c("Pleasant", "Long", "Plainfield")