Added basic handling of a shared ref into a get_local
Modified fibonacci example to add an example of a trait, albeit a bit silly :)
Made a safe wasm::print_i32 and modified the examples to use it instead of
the unsafe extern directly (which still works)
For the print externs, MIR would have the result of the Rust call set into
a local but the wasm functions return void. Detecting this case has been
simplified, without looking at the local to see if it was of the unit type
get_localwasm::print_i32and modified the examples to use it instead of the unsafe extern directly (which still works)