Add vim-repeat plugin

Repeat.vim remaps `.` in a way that plugins can tap into it. With this
plugin you can, for instance, repeat commands from surround.vim.
Change rename.vim to Tim Pope's vim-eunuch

Does what rename.vim does (`:Move` or `:Rename`) **plus**:

* Adds `:Unlink` or `:Remove` to delete the current buffer + file
* Adds `:Mkdir` (with no argument, create the current file's containing
  directory)
* Adds `:SudoWrite` if you forget to edit a file as root
* Automatically chmods a file to `+x` if it starts with `#!`
* Tim Pope! :heart:
Force vertical diffs

Fugitive was updated to switch to horizontal diffs on narrow screens.
Everyone I've seen experience this behavior finds it disorienting. This
setting forces a vertical diff without users having to use different
shortcuts to enter diff mode.
Add zshenv file

From the [Zsh manual](http://zsh.sourceforge.net/Intro/intro_3.html):

> '.zshenv' is sourced on all invocations of the shell, unless the -f option is
> set. It should contain commands to set the command search path, plus other
> important environment variables. `.zshenv' should not contain commands that
> produce output or assume the shell is attached to a tty.

Why is this important? [Alfred](http://www.alfredapp.com/) workflows run in
non-interactive shells. When the `$PATH` is set, or `rbenv` is initialized, in
`zshrc` instead of `zshenv`, those workflows will not use the correct Ruby
version and might not have access to certain bin files, such as those from
`$HOME/.bin/` or Homebrew.
Remove old doc directory

Resolves #276
Document vim-mkdir in README
Use `gh`, not `hub`

[gh] is a [hub] reimplementation that's much faster and is now the official
Github CLI. It appears that "hub" is [deprecated].

[gh]: https://github.com/jingweno/gh
[hub]: https://github.com/github/hub
[deprecated]: github/hub#475

Matches thoughtbot/laptop:

https://github.com/thoughtbot/laptop/commit/d9a9dfe09bf5898172c752c87be7c5ae6537c5f2
Remove unused plugins after rcup

Running `rcup` should remove any plugins that are no longer in use. For
instance, we recently replaced `rename.vim` with `eunuch`. `rcup`
installs the new plugin but does not clean up `rename` from the plugins
directory. The addition of `PluginClean!` does this (without
confirmation).
Fix the zsh config glob

The glob used a modifier, but it was modifying a directory instead of a
glob that matched all the files in the directory. Add the missing `*` to
fix this.
Include local gitconfig at the end of .gitconfig

Allows for customizing git's commit message template and overriding fetch.prune.
Prevent evil nbsp from being invisible

Not seeing these can be problematic, since you won't know what broke your code on the day that one of them sneaks in.

Here's a few other common characters people use for this: https://github.com/search?utf8=%E2%9C%93&q=nbsp%3A+extension%3A.vimrc&type=Code&ref=searchresults
Updating readme to use thoughtbot/formulae

Brew bundle is deprecated. fixes #309
Removes Brewfile, no longer needed
Ignore tags file, but not directories named tags
Wrap at 72 characters for git commit messages

The body of a git commit message is conventionally ([1], [2]) wrapped at
72 characters. This commit adjusts .vimrc to automatically wrap the body
of git commit messages at 72 characters.

[1]: http://robots.thoughtbot.com/5-useful-tips-for-a-better-commit-message
[2]: http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html
Add /usr/local/sbin to PATH

Some homebrew formulae, (e.g. [RabbitMQ][1]) link binaries here.

[1]: https://github.com/Homebrew/homebrew/blob/master/Library/Formula/rabbitmq.rb
Reorganize how `rbenv` is setup

Since `.zshenv` is where the PATH is modified, unless `$HOME/.rbenv/bin`
is placed in the path in this file, it won't ever get loaded. Instead of
checking for `rbenv` presence with `which`, check if `$HOME/.rbenv`
exists. If so, update `$PATH` and initialize.
Setup `nvm` in `zshenv`
Add local overrides
Add dotfiles not in upstream