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/cdsl/isa.py

@@ -469,7 +469,7 @@ class Encoding(object):
                 "Format {} must match recipe: {}".format(
                     self.inst.format, recipe.format))
 
-        if self.inst.is_branch:
+        if self.inst.is_branch and not self.inst.is_indirect_branch:
             assert recipe.branch_range, (
                     'Recipe {} for {} must have a branch_range'
                     .format(recipe, self.inst.name))