The magic variables '$~' and '$?' are now method-local and concurrent-safe. 'Tuple' is now correctly considered a struct. 'Pointer' is now correctly considered a struct. Renamed 'Function' to 'Proc'.

Added Tuple#clone and Tuple#dup. Faster tuple methods by using macros. Tuple#length and Tuple#[](index) (with a runtime index) are no longer primitives and are now implemented in Crystal.