Add code to expand file processing

[larsvilhuber]

We have code for R and for Stata to read files.

• Standardize the output (Steps 2 and 3)
• Also parse Stata files for missing variable labels (Step 2) and summarize
• Add the output to the REPLICATION.md as a summary (Step 4)

[larsvilhuber]

This is mostly done. Moved the incomplete part (labels) to #23