Add feature to filter register by venue

[angelina-momin]

Resolves issue #46

Related to changes in register: https://github.com/codecheckers/register/pull/64

This PR has a lot of major changes. Ideally I would have liked fewer changes but I needed to refactor, rewrite a significant amount of code for this new feature. As a result I think the following PR's will be shorter as less will need to be refactored to put in changes.

The following changes were made:

• Bumped version to 0.2.0
• register.R and render utils functions now creates separate registries for each venue.
• Created utils_register_sort.R. It has the utility function create_list_venue_sorted_register_tables
• Removed add_repository_links from preprocessing to keep the links generic format. Instead the repository links are now added dynamically when rendering the md and html files. This way "register" will not need to be passed each time.
• In R-CMD-check.yaml, configured GitHub Action R package build so that it throws error on error only and not with warnings.
• As R does not have dynamic scoping, I added global config CONFIG in register.R to avoid defining too many arguments for each function. I will consider refactoring later on if I can find an alternative to using globals.

[angelina-momin]

Still need to fix issue regarding hrefs in the margin of the sorted registers' html files

[nuest]

@angelina-momin Good job!