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/meta-python/base/settings.py

@@ -166,4 +166,13 @@ probestack_size_log2 = NumSetting(
         """,
         default=12)
 
+#
+# Jump table options.
+#
+jump_tables_enabled = BoolSetting(
+        """
+        Enable the use of jump tables in generated machine code.
+        """,
+        default=True)
+
 group.close(globals())