Enable usage of FuzzyTermQuery for specific fields via QueryParser (#1750)

* Make nightly Clippy mostly happy.

* Document how to produce TermSetQuery queries using QueryParser.

* Enable construction of queries using FuzzyTermQuery via the QueryParser

* Use FxHashMap instead of HashMap in the QueryParser as these hash tables are not exposed to DoS attacks.

* Use a struct instead of a tuple to improve readability.

src/schema/text_options.rs

@@ -258,7 +258,7 @@ mod tests {
         let field = schema.get_field("body").unwrap();
         let field_entry = schema.get_field_entry(field);
         assert!(matches!(field_entry.field_type(),
-                &FieldType::Str(ref text_options)
+                FieldType::Str(text_options)
                 if text_options.get_indexing_options().unwrap().tokenizer() == "default"));
     }