caltechlibrary/convert_codemeta: First release of convert_codemeta

convert_codemeta validates and converts codemeta.json files from different formats using the codemeta crosswalk table. The design of this package is inspired by codemetar, but adds support for converting nested elements using a dotpath in the crosswalk table. It also demonstrates how more complex format conversions (mapping with logic) can be added into the package.