Backport PR
#4232: no highlight if no language specified...
Backport PR
#4232: no highlight if no language specified
This matches behavior of places like GitHub, where if you do not specify a language, e.g.
```
no_highlighting("here")
```
There is no syntax highlighting. You must do
```python
def foo(a="hi"):
return 5
```
to enable highlighting in a particular language.
With configuration as it is right now in IPython, it is impossible to disable syntax highlighting in markdown blocks.
