fix bug

[2014/02/26]

#### Bug
1. [index](http://127.0.0.1:5000/index/) shows the files, but the name
and link is wrong. ![wrong name](progress/pic/wrong.png =100x)
	2. The URL has only first and last item.

##### Why?
1. The index is processed in `wiki#index()` method.
2. ![why1](progress/pic/why1.png =200x): name has the name of the
markdown file, and the path_prefix has all the path information.
3. ![why2](progress/pic/why2.png): url creation only uses only first
part of path.
	4. [-3] removes the *.md* from the name.