R Support [WIP]

[ForgottenProgramme]

Fixes #306

Add CRAN origin to Grayskull. These changes only aim to handle simple R recipes. The functionality to extract compiler information from R metadata and therefore handle complex packages will be added in consequent iterations.

ToDo

• [ ] Write unit tests
• [x] Extract and add License
• [x] cran metadata in commented form at the bottom [I am able to add it at the top. not at the bottom]
• [x] r prefix in package name at top
• [x] source: section of the recipe (urls and sha256)
• [x] requirements: host and requirements: build
• [x] Hardcode rpaths:
• [x] set posix and set native at top
• [x] Add r-base to host and run requirements everytime
• [x] reorder the requirements to be sorted. NOTE: (It is not a requirement to have the packages listed in a sorted order. But it's a nice to have, as it improves readability for users trying to look for a specific package in the list)
• [ ] build:
• [ ] requirements: build:
• [ ] in source: section, the 'url' needs fixing

[ForgottenProgramme]

[ForgottenProgramme]

@marcelotrevisani

[marcelotrevisani]

Closing this in favor of https://github.com/conda-incubator/grayskull/pull/423

Thank you very much for your hard work and all effort that you put into this!