setup: Create script for zsh setup.
setup: Fix typo in setup utility library.
hg: Create topic folder for Mercurial.
setup: Separate out lists of link sources.
readline: Create topic folder.
git: Create topic folder.
setup: Don't support custom install locations yet.

Some of the dotfiles assume that they are located in the user's home
directory. Let's not support installing to custom locations until we
sort that out.
zsh: Bring back the alternative ZDOTDIR.

This will make it simpler to add topic-based zsh customization. The zsh
startup files will source relevant files from appropriate locations
within ZDOTDIR, and anything that wants to add behavior will just have
to add their customizations to the proper directory.
zsh: Put Colemak ZLE tweaks into the Colemak topic folder.

Also augment .zshrc to pick up any customizations in
$ZDOTDIR/interactive.
tmux: Put tmux Colemak keybindings into Colemak topic folder.
readline: Move customizations to Colemak topic folder.

Everything in inputrc is for Colemak, anyway.
tmux: Move customizations into a topic folder.
tmux, zsh: Move relevant customizations into tmux module.
lynx: Move key remappings into Colemak module.
lynx: Move customizations into new topic folder.
tmux: Look in ~/.coleslaw for Colemak keybindings.

It'll probably be easier in the long run to have most Colemak-related
customizations be in a single directory.
zsh: Use "zsh_history" instead of ".zsh_history".

Now that history isn't stored in $HOME, there's no real reason keep it
hidden.
setup: Don't allow custom target.

I have no idea how this is going to work yet, so we'll just leave it out
for now.
setup: Pass "args" to sub-scripts via environment.

Turns out that POSIX:2004 doesn't require shells to pass arguments to
sourced scripts. Let's use the environment instead.
setup: Allow custom install locations.

Well, sort of. The subscripts now take into account the environment and
positional parameters before deciding where to install stuff. There are
still some kinks to work out.