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/cfg_printer.rs

@@ -48,8 +48,11 @@ impl<'a> CFGPrinter<'a> {
                     BranchInfo::SingleDest(dest, _) => {
                         write!(w, " | <{}>{} {}", inst, idata.opcode(), dest)?
                     }
-                    BranchInfo::Table(table) => {
-                        write!(w, " | <{}>{} {}", inst, idata.opcode(), table)?
+                    BranchInfo::Table(table, dest) => {
+                        write!(w, " | <{}>{} {}", inst, idata.opcode(), table)?;
+                        if let Some(dest) = dest {
+                            write!(w, " {}", dest)?
+                        }
                     }
                     BranchInfo::NotABranch => {}
                 }