Refactor primary expressions

[savq]

• Add _quotable rule for expressions that can be quoted without extra parentheses and disallow arbitrary expressions in quotes and interpolations.
• Add quote and interpolation expressions to _primary_expression.
• Add field names to values in field, index and parametrized types expressions.
• Replace parameterized_identifier with parametrized_type_expression:
  • Remove type_argument_list
  • Allow any _primary_expression to be parameterized
  • Allow subtype clauses (unary <:) in type arguments
  • Allow empty type argument list (e.g. Tuple{})
• Rename subscript_expression to index_expression.
• Fix parenthesized expressions allowing arbitrary blocks.
• Fix identifiers allowing @.
• Add more tests for primary expressions: fields, indices, curly, quotes and interpolations.
• Remove 12 files from known failures.

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• closes #10
• closes #69
• closes #49. Restricting quotables fixes the parsing problem listed in the issue. However, this doesn't improve #11, so changing the precedence of the colon_quote might still be necessary.