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You can now do

    'xxx'.Length

Also of note:

- `new_lines_opt` was effectively eliminated from the grammar, by defining it as `Empty`. I intended this to be temporary, to make it easier to analyze shift/reduce conflicts. But when all tests continued to pass, I decided to leave it in.

- Added a bunch of parser tests from the examples in the language spec. They only test that the parser accepts the input, not that produces the right parse tree.