Use sphinx for generating documentation

This adds sphinx based documentation generation.  For now,
this manily renders some introduction and the autodoc-genreated
class/method reference from the source code for our libraries.

Actual user-level documentation for pySim-{prog,shell,read} remains
to be added separately

Change-Id: I52603e93c2c129a9e79687da6c534fa56a40a649
diff --git a/docs/legacy.rst b/docs/legacy.rst
new file mode 100644
index 0000000..492be46
--- /dev/null
+++ b/docs/legacy.rst
@@ -0,0 +1,2 @@
+Legacy tools
+============