Minor tweaks

[krlmlr]

• Minor documentation updates to ?fansi
• Explicit tests for R 3.1 till 3.5
• Putting .Rproj under version control (happy to remove this commit if you feel strongly about it)

[brodieG]

Thanks @krlmlr. Since this is the first PR I would accept I need to check a couple of things. But before that, a few comments / questions:

1. Is it really necessary to add the .Rproj business? I don't use Rstudio personally so it seems like clutter. Is there a specific reason to do this that is good globally? I don't feel too strongly about it, but would want a good fundamental reason to do this.
2. You probably realize this already, but adding the tests for all the 3.x versions would not have caught this as the problem version is 3.2.1 and Travis 3.2 tests against 3.2.5. I'm a little reluctant to add so many versions mostly because I feel like I'm hogging resources. Maybe there is a way to set this up conditionally so all versions are only run against a merge on specific branches, and then run the normal set (dev/rel/oldrel) on the dev branch (probably there is, but I'm not a .travis.yml wizard). Aside: this problem happened because R-core changed the API within an R release cycle, which seems wrong.
3. Are you able to make the pull request from / to the 'development' branch? Master branch is kept in sync with CRAN. All my development is done off of branches from 'development', and then eventually everything gets merged into CRAN.

If this all feels like too much of a PITA to you (and I understand if it does) I can easily make some of the modifications here when I fix the 3.2.1 issue.

[krlmlr]

Thanks, I've removed the first commit (due to lack of reason other than convenience) and sent two separate PRs against master and development. Note that the development branch currently seems to lag behind master.

[krlmlr]

The auto-cancellation setting helps reduce resource consumption on Travis (https://docs.travis-ci.com/user/customizing-the-build/#Building-only-the-latest-commit), as does the fast-finish setting (https://docs.travis-ci.com/user/customizing-the-build/#Fast-Finishing).

[brodieG]

Thanks for the hints re: travis. I'll review and plan to merge in absent other issues this coming week when I fix the 3.2.1 problem.