Import prezto into dotfiles.

Prezto is checked out into the default directory '~/.zprezto',
and its accompanying rc files are copied to 'zsh' directory.
Custom theme 'wook' on top of prezto zsh framework.

* 'dotfiles/zsh' is now sym-linked into '~/.zsh'.
* Enables git and vi-mode modules(plugins).
* Enables custom-located zsh script to work with prezto.
* Custom prompt theme 'wook', based on sorin's theme,
  is added and configured by myself. (more to improve)
Support <Ctrl-R> history search key bindings

'key-binding.zsh' defines the bash-compatible behavior
on <Ctrl-R> (backward history incremental search).

Now zshrc sources all the after-prezto zsh files
located in the directory 'zsh/zsh.d'.
Relocate fpath settings from zshrc to zshenv

Since zshrc is the first file that zsh reads,
it's the right place for environmental settings
such as fpath (locations for custom zsh settings)
Set EDITOR=vim (zshenv)
Add Ruby & RVM support on zsh settings

* Enabled prezto module 'ruby'
* Add rvm version info (if any) on PROMPT
Add Python & virtualenv support on zsh settings

* Enabled prezto module 'python'
* Add virtualenv info (if any) on PROMPT
* Two environent variables, python path and additional
  arguments for virtualenvwrapper are given (see zshenv)
Remove accidentally added rvm PATH settings

This is totally unnecessary, since we are powered by prezto.
Merge branch 'prezto'
Use spaces for indenting install.py