Add highlighting support for range, return type and pattern binding operators

[ghost]

Hello there.

I have made some additions to the grammar matching rules to include:

• Range operators (.., ...)
• Function and closure return type operators (->)
• Pattern name binding operator (@)

The additions should be compatible with #59, which attempts to refactor a single operator match rule into multiple ones with better semantics.

Sample test snippets for highlight checking have also been added to the test.rs file.

Also, just as a suggestion, it might be worthwhile refactoring a certain set of the operators under a common repository to reduce the number of individual includes required in some of the broader match rules like the one for function definitions.