* Add fuzzing support
See fuzz/README.md for details. Example bug: #725
* improve fuzz docs
* fuzzing: make relevant config part of input
Most of the config is to do with what files to parse, however
one setting - treat_doc_strings_as_comments - does impact parse_from_slice
* fuzzing: improve docs + config clarity
* fuzz/README.md: install instructions + another todo item