My takeaways from working with this grammar

[digitcrusher]

This is a pull request of a few fixes I had to apply while adapting this grammar for my text editor. Here's some reasoning behind each commit, from oldest to newest:

1. The first commit slashes a dozen individual queries to match function parameter names into just one. This closes Difference in fields between parameters #199.
2. Classifying assignment statements as expression statements is not only wrong (Python 3, Python 2) but also introduces an unnecessary level of indirection when querying for class attribute declarations.
3. as_pattern already has an alias field. This change brings _as_pattern into line.
4. Free stuff. Discriminating member identifiers is necessary to ensure lambda foo: foo == obj.foo produces the correct result. The only other solution is to capture expression as local.reference instead of identifier but that produces a lot of useless matches.
5. Self-explanatory.