Turn present.vim into presenting.vim :)

Add a bunch of functionality
 - work with rst
 - work with markdown
 - work with org
 - presentation view is nicer (no numbers, cleaner/smaller statusline)
rename present.vim to presenting.vim
Use normal! instead of normal.
Use global for the slide separator list.
Rename StartPresent to StartPresenting.
Rough draft of the documentation.
Format doc.
Nice README.rst
Some simple slides for the supported file types.