The point of this branch is the second commit that changes
validate_asciidoc.sh. The first one is taken from another PR and should
not be reviewed.
The previous version of the validation could handle the following case:
```asciidoc
:path: path/to/file.adoc
include::{path}[]
```
This new validation also adds support for the case of a variable inside
a path:
```asciidoc
:language: csharp
include::rules/S1000/{language}/file.adoc[]
```
83c54f9795