Such errors are raised when SyntaxError nodes are executed, and are also
used for internal control flow.
The 'break' and 'continue' commands are currently only allowed inside
for loops, and outside function bodies.
This also adds a 'loop' keyword for infinite loops.
Now that fonts know their own weight, we no longer need highlighters to
tell us which font to use. Instead, they can just say "this should be
bold" and we'll find the right font ourselves.
This fixes the wrong highlight behaviour when a newline is used as
sequence separator:
```sh
echo foo
if foo {}
^ This character would previously be bold
```
