[docs] significant revamp - add sphinx support

make it possible to compile documentation via sphinx - main change is to
use RST instead of MarkDown for most files.

docs/development/index.rst

@@ -0,0 +1,16 @@
+Developer's Guide
+============================================
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Contents:
+
+   module
+   theme
+
+Indices and tables
+==================
+
+* :ref:`genindex`
+* :ref:`modindex`
+* :ref:`search`