添加上下方向键的支持
update freshman.md add 开始，讨论，贡献
add animate for section changing
add uyan comment
update md
fix a small bug
update doc.comment for uyan
add doc.bg() method && remove some useless code && add sectionReady()
add epub && mobi
add img[alt=background-width]
update styles
remove pdf
add X-UA-Compatible
change UTF-8 meta order