Updated get-clean-data-proj run_analysis.R

- Now filters out the features not used in the project
- Now converts feature names to descriptive names
Updated get-clean-data-proj Codebook

- Added footnote about features.txt containing duplicate
  feature names
- Added a description of the descriptive names used in
  this project
- Added a column to the table to show the original feature
  names along with the descriptive names used