Add new command `prelude-top-join-line`

Saner version of the built-in `join-line`, that joins lines from the top
to the bottom.
Recompile the Prelude dir on `prelude-update`
Vanity URL for the installer

Made with
`https://github.com/bbatsov/prelude/raw/master/utils/installer.sh`

More info: https://github.com/bbatsov/prelude/raw/master/utils/installer.sh
Use valid shell commands

By not prepending `$` to your examples users can copy them easier
without fear of seeing `bash: $: command not found` or similar
Merge pull request #333 from joshuarh/vanity-url

Vanity URL for the installer
Merge pull request #334 from joshuarh/valid-shell-commands

Valid shell commands
Bind prelude-top-join-line to C-^
Merge branch 'master' of github.com:bbatsov/prelude

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Bind prelude-top-join-line to C-^
  Use valid shell commands
  Vanity URL for the installer
  Recompile the Prelude dir on `prelude-update`
  Add new command `prelude-top-join-line`
Fix #337 - don't promt for sudo passwd for non-existing directories
up
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Fix #337 - don't promt for sudo passwd for non-existing directories