* Add 'jump_table_entry' and 'indirect_jump' instructions.
* Update CodeSink to keep track of code size. Pretty up clif-util's disassembly output.
* Only disassemble the machine portion of output. Pretty print the read-only data after it.
* Update switch frontend code to use new br_table instruction w/ default.
* Mark emit_to_memory as unsafe, and provide a safe compile_and_emit.
Mark `Context::emit_to_memory` and `MemoryCodeSink::new` as unsafe, as
`MemoryCodeSink` does not perform bounds checking when writing to
memory.
Add a `Context::compile_and_emit` function which provides a convenient
interface for doing `compile` and `emit_to_memory` in one step, and
which can also provide a safe interface, since it allocates memory of
the needed size itself.
* Mention that `MemoryCodeSink` can't guarantee that the pointer is valid.
