zohooo

看到 `filter-branch` 觉得很亲切，之前拆分 ctex-doc 时用过并记录了使用过程： https://github.com/CTeX-org/ctex-doc/issues/4#issuecomment-96192542 根据之前 @leo-liu 的看法，有些子项目有依赖关系，不适合拆分开。其他的我认为拆开来更方便维护。

I have tried latest code in beamer repository, but didn't fixed this problem.

I comared `listings` version 1.6 and 1.7, and found that a `\leavevmode` was added to the beginning of lstlisting environment in version 1.7, causing the problem in `beamer` frames. ````latex...

@tertium You could also use `\lstnewenvironment` to define your own listing environments. These environments work as before, without extra vertical space.