R script that does the following:
# Downloads and extracts data
# Merges the training and the test sets to create one data set.
# Extracts only the measurements on the mean and standard deviation for each measurement.
# Uses descriptive activity names to name the activities in the data set
# Appropriately labels the data set with descriptive activity names.
# Creates a second, independent tidy data set with the average of each variable for each activity and each subject.