[Fix #434] Correct ambiguity in the use of the term keymap
[Fix #411] Add Homebrew module
[Fix #452] Squash bugs introduced in fcab2a1
[Fix #459] Correct typos in the dpkg module
Increase control over multiplexer auto-start

Setting the auto-start 'remote' and 'local' zstyles for the screen and
tmux modules to 'true' automatically starts a session in SSH connections
and in local terminals respectively.

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Move from Carton to Cask

Carton was renamed to Cask to avoid a name clash with a Perl utility of
that name.
Clarify customization instructions

Explicitly state that a new user must create his own fork to commit and
track changes via Github.

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Update external completions
Update external history-substring-search
Update external syntax-highlighting
Fix lesspipe.sh detection in custom PATH

The detection of lesspipe.sh has to be done after setting PATH as it
could be installed in a non-standard bin directory. For example,
Homebrew installs lesspipe in /usr/local.
[Fix #383] Do not set $MANPATH

man dynamically searches for man pages based on $PATH.
[Fix #381] Remove the path_helper workaround
Use $GNUPGHOME in GPG agent startup

Use the value of $GNUPGHOME, to facilitate moving GPG's home.

This lets users who keep their GPG keyring on external devices or alternate
folders use the gpg-agent autostarting, even if $HOME/.gnupg does not exist.
Add Emacs module

Enables Emacs dependency management with Carton.