Panic support

[carlpaten]

Rust implements "panics" (equivalent to C++ exceptions). They're used throughout the standard library, including when allocating memory through Box::new.

To support panics, we need to implement ::rt::begin_unwind and possibly ::rt::begin_unwind_fmt. A good first implementation would print to the emergency console and immediately crash.

Enables:

• Basic Memory Allocation #33

[carlpaten]

I believe this worked before the Rust compiler switched from rust_begin_unwind to rust_fail. Fixing in M3.

[kanetkarster]

Based off a recommendation from "Set Up Rust" we'll focus on adding this feature later. Currently, panicking will simply print an error message as CRust closes