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.
.vimrc: Avoid creating backups when editing files in `/tmp`

See http://vim.wikia.com/wiki/Editing_crontab.
.aliases: Remove the now-broken `whois` alias

Closes #397.