#' \item has one column of all state abbreviationis (all caps, including \code{DC} or a column of state names (standard capitalization) named \code{state}
#' \item has another column of values named \code{value}
#' }
#'
#' Doing so will create a "statebin" chart with 5 breaks and return a \link{ggplot2} object.
#'
#' You can use a different column for the state names and values by changing \code{state_col}
#' and \code{value_col} accordingly.
#'
#' To add a title, change \code{plot_title} to anything but an empty atomic string vector (i.e. \code{""})
#' and set \code{title_positioin} to "\code{top}" or "\code{bottom}". Choosing "\code{bottom}"
#' will cause \code{statebins} to use \link{arrangeGrob} to position the title via \code{sub} and
#' return a frame grob instead of a ggplot2 object.
#' @param state_col column name in \code{state_data} that has the states. no duplicates and can be names (e.g. "\code{Maine}") or abbreviatons (e.g. "\code{ME}")
#' @param title_position where to put the title ("\code{bottom}" or "\code{top}" or "" for none); if "\code{bottom}", you get back a grob vs a ggplot object
#' Create ggplot-based "statebin" charts in the style of \url{http://bit.ly/statebins}
#'
#' \code{statebins()} creates "statebin" charts in the style of \url{http://bit.ly/statebins}
#'
#' This version uses a continuous scale based on \link{RColorBrewer} scales
#' (passing in a 6 element \code{RColorBrewer} palette to \link{scale_fill_gradientn}).
#'
#' The function minimally expects the caller to pass in a data frame that:
#'
#' \itemize{
#' \item has one column of all state abbreviationis (all caps, including \code{DC}) or a column of state names (standard capitalization) named \code{state}
#' \item has another column of values named \code{value}
#' }
#'
#' Doing so will create a "statebin" chart with 5 breaks and return a \link{ggplot2} object.
#'
#' You can use a different column for the state names and values by changing \code{state_col}
#' @param state_col column name in \code{state_data} that has the states. no duplicates and can be names (e.g. "\code{Maine}") or abbreviatons (e.g. "\code{ME}")
#' @param title_position where to put the title ("\code{bottom}" or "\code{top}" or "" for none); if "\code{bottom}", you get back a grob vs a ggplot object