Change default branch to master.

[waciumawanjohi]

The default branch is currently dev. However, most projects use master as the default branch. This naming convention is baked into git. "the git init command creates [the master branch] by default" Pro Git

Following wide spread convention makes it easier for newcomers to contribute.

Any objections to fast-forwarding the master branch to the current state of the repo and making it the default? Objections to deleting the dev branch? (Dev could be resurrected for a grand rewrite, for example setting v9 in markdown)

Keeping this issue open for a week.

[xxylem]

This seems a reasonable change that would aid new students. There have been no objections in the past month. I think we can go ahead with it.

[waciumawanjohi]

Done