Fix a bug in tex_skeleton.tex.
Added keymap for markdown.
Cos markdown bundle, plugin of markdown and html are loaded
simultaneously. Changed keymap of html to avoid the conflict.
Set tw=72 for tex file.
Changed nerdcommenter's left comment to <--- for markdown.
Tweaked config file for html.
Changed tex_9:

Now press <F2> could load a skeleton for beamer.
Added pairtools for css.
Config for cscope has done.