Move the 'meta' dir to 'lib/cretonne/meta'.

The 'lib/cretonne' directory will be the new root of a stand-alone
cretonne crate containg both Python and Rust sources.

This is in preparation for publishing crates on crates.io.

lib/cretonne/meta/test_srcgen.py

@@ -0,0 +1,8 @@
+from __future__ import absolute_import
+import doctest
+import srcgen
+
+
+def load_tests(loader, tests, ignore):
+    tests.addTests(doctest.DocTestSuite(srcgen))
+    return tests