Created mode for the "textile" markup language.

This mode is based off the documentation for ruby "Redcloth" library for the *Textile* markup language:

* [Writing Paragraph Text](http://redcloth.org/textile/writing-paragraph-text/)
* [Page Layout](http://redcloth.org/textile/page-layout/)
* [Phrase modifiers](http://redcloth.org/textile/phrase-modifiers/)
* [Attributes](http://redcloth.org/textile/attributes/)
* [HTML](http://redcloth.org/textile/html-integration-and-escapement/)

I am somewhat new to this domain and textile is pretty intricate, but hopefully this is a good start. One area that could use some attention is the stylesheet. I don't have a talent for aesthetics.