Tidy up Stata code format

[bvkrauth]

This should be strictly a code cleanup, and no change in functioning.

• [x] Run all do and ado-files through linter
• [x] Replace tabs with 4 spaces
• [x] Insert spaces between operators
• [x] Eliminate trailing spaces
• [x] Have (almost) all lines less than 80 characters
• [x] Replace implicit if conditions with explicit conditions
• [x] Eliminate semicolon as delimiter
• [x] Use descriptive names in loops
• [x] Always use ${ } to refer to global macros
• [x] Replace / comments / with * comments