.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.
.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.
.osx: Use `sudo` for `systemsetup`

Closes #415.
.osx: Disable the all-too-sensitive backswipe on Chrome

Closes #416.
Update URLs
.vimrc: Treat `.md` files as Markdown

`filetype` is set implicitly, without using setfiletype, because `*.md` is already associated with Modula-2 files and `setfiletype` doesn’t allow `filetype` to be set twice.

`setlocal` is used to apply a new `filetype` value for each Markdown file as it is being added to the buffer.

Fixes #418. Closes #419.
.functions: Add SNI support in `getcertnames`
Update URLs
.functions: Improve `getcertnames`
.gitconfig: Add alias to merge GitHub pull request

Ref. https://help.github.com/articles/checking-out-pull-requests-locally

Closes #422.
Brewfile: add some CTF tools

See https://github.com/ctfs/write-ups for more info.
Merge branch 'master' of github.jimb828:mathiasbynens/dotfiles

* 'master' of github.jimb828:mathiasbynens/dotfiles:
  Brewfile: add some CTF tools
  .gitconfig: Add alias to merge GitHub pull request
  .functions: Improve `getcertnames`
  Update URLs
  .functions: Add SNI support in `getcertnames`
  .vimrc: Treat `.md` files as Markdown
  Update URLs
  .osx: Disable the all-too-sensitive backswipe on Chrome
  .osx: Use `sudo` for `systemsetup`
  .aliases: Remove the now-broken `whois` alias
  .vimrc: Avoid creating backups when editing files in `/tmp`
  .bash_prompt: Interpret escape sequences correctly in all cases
  .bash_prompt: Add back escape sequences
  .bash_prompt: Avoid double-escaping ANSI codes
  Add `.editorconfig`
  .gitconfig: Add default Git `push.default` config