README: Update link to Lauri Ranta’s resources
.osx: Add SSD-specific tweaks

Source: http://forums.macrumors.com/showthread.php?t=1505922
.osx: Remove broken three-finger swipe commands

If anyone knows how to make this work, please let me or @necolas know!

Ref. #171.
.osx: Don’t `kill` Dashboard

`killall Dashboard` doesn’t actually do anything. To apply the changes for Dashboard, `killall Dock` is enough as Dock is Dashboard’s parent process.

Closes #277.
.aliases: Add `afk` to lock the screen

Closes #258.
README: Document the `.cask` file

Closes #280.
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  README: Document the `.cask` file
  .aliases: Add `afk` to lock the screen
  .osx: Don’t `kill` Dashboard
  .osx: Remove broken three-finger swipe commands
  .osx: Add SSD-specific tweaks
  README: Update link to Lauri Ranta’s resources