Create run_analysis.R

It accomplishes these five tasks:

o	Merges the training and the test sets to create one data set.
o	Extracts only the measurements on the mean and standard deviation for each measurement. 
o	Uses descriptive activity names to name the activities in the data set
o	Appropriately labels the data set with descriptive variable names. 
o	From the data set in step 4, creates a second, independent tidy data set with the average of each variable for each activity and each subject.