Fixing link to the docs.
See issue: https://github.com/igordejanovic/parglare/issues/57
- `ParseError` now has `symbols_expected`, `tokens_ahead` and
`symbols_before` attributes. See [Handling errors
- section](http://www.igordejanovic.net/parglare/handling_errors/).
+ section](http://www.igordejanovic.net/parglare/0.7/handling_errors/).
- 2018-05-24 Version 0.6.1
