v0.2.0

New release of the database with the following major changes:

• Clarified when the input and output CO2 measurements happened (and fix any error related to it)
• standardise the column names (no unicode characters anymore)
• Add metadata about variables in the readme + in a columns.csv file
• Add instructions for decompressing the database

Full Changelog: v0.1.0...v0.2.0