feat(RParser): improve handling of crandb package fields

[nokome]

crandb provides plenty of meta data for each package e.g. http://crandb.r-pkg.org/ggplot2

Currently, we don't handle every field or could handle them better e.g.:

• Title: assign to CreativeWork.headline ?
• Licence : should be parse the raw string into a schema.org URL or CreativeWork
• URL : if the URLS which point to a repo e.g. github.com then should be assigned to SoftwareSourceCode.codeRepository