Separate specification docs to another website about www.egison.org

[momohatt]

Progress on porting the 'Documentation' part of the homepage:

* Installation Manual
    * Install Egison in Mac
    * Install Egison in Linux
    * Install Egison in Windows
---> Done

* Emacs Mode
    * Emacs Mode for Egison
---> Not yet. Probably we can create a repo for emacs.el and write description in the README?

* User's Manual
    * Basics of Syntax and Semantics
    * Basics of Patterns : Syntax and Semantics
    * Pattern Matching
    * Matchers
    * Basics of I/O
    * Primitive Functions
---> Done

* Developer's Manual
    * Pattern-Matching Mechanism
---> Not yet

* Cheat Sheet
    * Egison Cheat Sheet
---> We have no plan to make one in the new reference

* Quick Reference
    * Egison Quick Reference
---> Deprecate

* Developement Status
    * ChangeLog on GitHub
    * Milestones
---> We can link these from www.egison.org?

* Others
    * Concept of Egison
    * History of Egison
    * FAQ
    * Egison Command Line Tutorial
---> We can leave these in www.egison.org