Generate libvirt constants from libvirt sources.

- Add a yacc-based parser and a hand-written lexer to read the
remote_protocol.x file from libvirt's sources.
- Use the new parser to generate the constants used to communicate with
libvirt.

internal/lvgen/.gitignore

@@ -0,0 +1,4 @@
+# Ignore the yacc intermediate files.
+y.go
+y.output
+