This patch makes `HTMLOutputFormat` correctly escape all < and > characters
that occur in source code. Otherwise, a web browser rendering the resulting
HTML will interpret those characters as tags.
This patch fixes syntax highlighting for the following scenario:
```
Type<GenericType>.call()
```
Highlighting generic types is especially tricky, since we want them to
be highlighted when appearing at the call site, like above - but we don’t
want to highlight them when they are being declared. Hopefully with this
fix all/most edge cases are covered.