move to ctex from bare CJK/xeCJK

* base on ctexbook. Use UTF8 option. Thus can compile with pdflatex.
  (Note that GBK support is to be verified.)
* fontname.def use standard xeCJK syntax. Note it will be used
  only when nofonts option is specified and when xelatex is used.
thuthesis.dtx: fix title font with pdflatex

* ctex use YouYuan as the Chinese sans-serif font, which is not desired
  in the template.
main.tex: add explanation for *fonts options
thuthesis.dtx: walkaround no footnote mark issue