add support for having raw slashes `/` in $slug

e.g. in config/config.toml
```
[[timelines]]
name = "category/subcategory"
file = "titles.txt"
```
in config/titles.txt
```
2014-07-25 17:41:46+0800 // Hello, world! // tutorials/hello
This is the first lesson for you.
```
update templates for last commit