Implement jump tables (#453)

* 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.

lib/codegen/src/write.rs

@@ -443,7 +443,17 @@ pub fn write_operands(
             write!(w, " {} {}, {}, {}", cond, args[0], args[1], destination)?;
             write_ebb_args(w, &args[2..])
         }
-        BranchTable { arg, table, .. } => write!(w, " {}, {}", arg, table),
+        BranchTable {
+            arg,
+            destination,
+            table,
+            ..
+        } => write!(w, " {}, {}, {}", arg, destination, table),
+        BranchTableBase { table, .. } => write!(w, " {}", table),
+        BranchTableEntry {
+            args, imm, table, ..
+        } => write!(w, " {}, {}, {}, {}", args[0], args[1], imm, table),
+        IndirectJump { arg, table, .. } => write!(w, " {}, {}", arg, table),
         Call {
             func_ref, ref args, ..
         } => write!(w, " {}({})", func_ref, DisplayValues(args.as_slice(pool))),