Relaxes random block parsing rules by switching to an HTML parser. Adds
support for up to 10 levels of nested random blocks. Adds new
`prompt_randomizer_log_level` parameter in `config` file.

```
<random count="2" allow-repeat="false">
  <option weight="2">Apple $10</option>
  <option weight="1">Banana $5</option>
  <option>Cherry <random><option weight="2">$2</option><option weight="1">$1</option></random></option>
</random>
```