add background image

 On branch dev
	modified:   source/css/_base/layout.styl
	new file:   source/img/background.jpg
change header font color to FFFFFF

 On branch dev
	modified:   source/css/_partial/header.styl
change footer font color to white

 On branch dev
	modified:   source/css/_base/variable.styl
change article backgroud to transparent

 On branch dev
	modified:   source/css/_partial/article.styl
change article font color to white

 On branch dev
	modified:   source/css/_base/variable.styl
change link color to BEDEEA

 On branch dev
	modified:   source/css/_base/variable.styl
change silderbar background to transparent

 On branch dev
	modified:   source/css/_partial/sidebar.styl
change commit background to transparent

 On branch dev
	modified:   source/css/_partial/comment.styl