Fix issue #510: Support text blocks in Diet templates

Fix issue #510

Redo of https://github.com/rejectedsoftware/vibe.d/pull/514 (which history got screwed up ;) )

Added tests for cases mentioned by Sönke

```
Some care needs to be taken to handle anything after the dot correctly:

    pre.test -> <pre class="test">
    pre.test. -> <pre class="test"> + block text
    pre. test -> <pre> + block text (jade apprently ignores the "test" in this case
    pre(). -> <pre> + block text
```