Refactors the invoke syntax of a runtime to be simpler and with less magic.

Previously calling a mun function looked like:

let runtime_ref = runtime.borrow();
let arg: i64 = invoke_fn!(runtime_ref, "arg", a, b).unwrap();

WIth this MR this becomes:

let runtime_ref = runtime.borrow();
let arg: i64 = runtime_ref.invoke("arg", (a,b)).unwrap();

Arguments are passed in as a single tuple. No more macros. A single entry point to call functions which is also properly suggested by language servers and the like. And the code became much simpler. The only downside is that calling a function with a single argument requires a bit of strange rust syntax: (a,). Note the comma. Without it, the parentheses are seen as an expression instead of a tuple declaration.