Rename branches to updated general defaults used.

[e-lo]

As a contributor, I'd like to expect consistent naming in my branches across repositories. Current general defaults across github are:

• main (previously master)
• develop

See: https://github.com/github/renaming

[e-lo]

cc: @joecastiglione on if community would like me to implement.

[ssmith55]

Other users, notably AequilibraE, are using the current directory structure in some examples. I am fine with this change, but would like to save it for the next release, with advance notification to the user community.

[pedrocamargo]

Excellent suggestion

[ssmith55]

Renamed the development branch to develop. Git code for your local environments:

git branch -m development develop
git fetch origin
git branch -u origin/develop develop
git remote set-head origin -a