Generate encoding tables. (WIP).

Amend build script to generate an encodings-<isa>.rs file for each target ISA.

Emit a function that can evaluate instruction predicates.

Describe the 3-level tables used for representing insrruction encoding tables.
Add Python classes representing the tables.

The generated code is incomplete and not used anywhere yet.

meta/srcgen.py

@@ -51,12 +51,21 @@ class Formatter(object):
         self.indent = self.indent[0:-self.shiftwidth]
 
     def line(self, s=None):
-        """And an indented line."""
+        """Add an indented line."""
         if s:
             self.lines.append('{}{}\n'.format(self.indent, s))
         else:
             self.lines.append('\n')
 
+    def outdented_line(self, s):
+        """
+        Emit a line outdented one level.
+
+        This is used for '} else {' and similar things inside a single indented
+        block.
+        """
+        self.lines.append('{}{}\n'.format(self.indent[0:-self.shiftwidth], s))
+
     def writelines(self, f=None):
         """Write all lines to `f`."""
         if not f: