Load and preprocess the data
Calculate mean total steps taken per day
Look at the average daily activity pattern
Impute missing values
Compare weekday and weekend days
Plot total number of days with imputed data set

The instructions asked to replot the histogram of the total daily steps,
not the average daily activity.
Remove NA values when summing
Add analysis to imputed data section
Suppress messages when loading `dplyr'
Include mean and median values in text