.gitconfig: Add default Git `push.default` config

Use the backwards-compatible `matching` setting by default. On machines with newer Git installations, it avoids the annoying Git warning, and it can be overriden to use `simple` instead in `~/.extra`.

Closes #400.
Add `.editorconfig`

See <http://editorconfig.org/>.
.bash_prompt: Avoid double-escaping ANSI codes

Fixes #399 and closes #402.
.bash_prompt: Add back escape sequences

Fixes #403.
.bash_prompt: Interpret escape sequences correctly in all cases

Closes #407.