Added `cast` class method to integer and float types. Use C::SizeT.cast(...) and C::ModeT.cast(...) instead of num.to_sizet and num.to_modet. Changed Pointer#memcmp to return an integer instead of a bool (like in C). Also added `zero class method.

Fixed bug: two different methods were having the same manging (one with &block and another without it but with the same type)

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.

Started implementing splats. Splat in def arguments are now working. Missing: combine them with default values and also allow splatting call arguments.

Fixed #154 and other constant-related bugs. Also: removed the "feature" of regex literals being automatically assigned to a constant to avoid multiple recompilations of the same regex (users must be able to choose that to)