Write docstrings derived from OpenSCAD manual

This change adds docstrings which are suitable for sphinx autodoc
generation.

The OpenSCAD User Manual is licensed under the
Creative Commons Attribution-ShareAlike License, and my research
suggests that it is safe to mix this with LGPL code.

These docs can be generated with

  tox -edocs

It would be very useful now for these docs to be hosted on
https://readthedocs.org/

Author: steveb

Diff for: Doc/index.rst

@@ -13,14 +13,17 @@ Contents:
 
 .. include:: ../README.rst
 
+Library Reference
+=================
+
+.. automodule:: solid.solidpython
+    :members:
 .. automodule:: solid
     :members:
 .. automodule:: solid.screw_thread
     :members:
 .. automodule:: solid.utils
     :members:
-.. automodule:: solid.solidpython
-    :members:
 
 
 Indices and tables

Diff for: README.rst

@@ -421,3 +421,8 @@ General Public License for more details.
 
 `Full text of the
 license <http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt>`__.
+
+Some class docstrings are derived from the `OpenSCAD User Manual
+<https://en.wikibooks.org/wiki/OpenSCAD_User_Manual>`__, so 
+are available under the `Creative Commons Attribution-ShareAlike License
+<https://creativecommons.org/licenses/by-sa/3.0/>`__.