Ability to customize zsh in ~/.yadr/custom/zsh folder

* Split zsh config into snippets in zsh/ folder, similar to vim
 * Feature implementation by @kylewest

* kylewest/zsh:
  Documentation for customizing ZSH.
  Only init fasd if it is installed.
  Removed brew and github plugins.
  updated .gitignore for new zsh paths.
  simplifying paths for zsh customization.
  added zsh aliases. Moved other files but left symlinks for backwards compatibility.
  automatically load RVM or rbenv.
  updated .gitignore
  adding sample zsh configs.
  added directories and code for custom zsh configuration.

zsh/fasd.zsh

@@ -0,0 +1,16 @@
+# only init if installed.
+if [[ -f $HOME/.fasd ]]; then
+  # Initialize fasd (https://github.com/clvv/fasd)
+  eval "$(fasd --init posix-alias zsh-hook)"
+
+  # aliases
+
+  # jump to recently used items
+  alias a='fasd -a' # any
+  alias s='fasd -s' # show / search / select
+  alias d='fasd -d' # directory
+  alias f='fasd -f' # file
+  alias z='fasd_cd -d' # cd, same functionality as j in autojump
+  alias v='f -e vim' # quick opening files with vim
+fi
+