.osx: Add Mac App Store section

- Move existing command to new section
- Add debug menu command

Ref. #150.
README: Recommend sourcing the bootstrapper

Thanks to @svnpenn and @nvartolomei in https://github.com/mathiasbynens/dotfiles/commit/a77f4872f26d681a35cface9d6bcb4ad55fec752#commitcomment-2100022, and thanks to @janmoesen for the BASH_SOURCE pointer.
.osx: Add command to remove all Dock icons
.bash_prompt: Use `tput setaf 0` for white

Using `tput setaf 0` instead of `tput setaf 256` makes sure that `WHITE` is white instead of the previous color.

Thanks to @rudolph9 for reporting this in #153.
bin: Update to Bash 4.2.39
.gitconfig: Set `push.default = simple`

This will be the default in Git v2.
.bash_prompt: Fix `parse_git_dirty` for Git v1.8.0+

Git 1.8.0+ says “nothing to commit (working directory clean)”.
Older Git versions return “nothing to commit (working directory clean)”.

Thanks to @nicolahery in #143 for the suggestion.
.aliases: Add `map`

Ref. #157.
.functions: Make `gz` more awesome
.aliases: Lowercase `com.apple.finder`

Hat tip: @alrra.
.osx: Show item info to the right of the icons on the desktop
.functions: Add `calc`
.bash_profile: Move the `LANG` & `LC_ALL` exports into `.exports`
.osx: Remove the iTunes Ping settings

Apple officially closed the iTunes Ping service on September 30th, 2012 (http://i.imgur.com/U7bHo.jpg).
.osx: Document the various values for Hot Corners settings
.osx: Clarify that the iTunes settings are for pre-iTunes 11 only
README: Update Lauri Ranta’s hidden preferences URL

The previous URL now 404s.
bin: Update to Bash 4.2.42
.osx: Fix typo

Ref. #183.
.functions: Add `getcertnames`

This function shows all the names (CNs and SANs) listed in the SSL certificate for a given domain.

As always, improvements and other feedback is welcome!