Removed symbolic links to data folder
Added data validation in run.sh and setup_database.sh

Prompt user to download data in the script if the data files do not
exist.
Bug fix in pipeline

The dependency in the pipeline has a bug. ext_clear_table must be
dependency for ext_people.
Fixed typos in data file names in walkthrough
Added documentation to compute recall script
Updated docs in improvement section
Updated extra section
Updated data downloading specification
Merge pull request #189 from HazyResearch/hotfix-docs

Hotfix docs