[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/other/NOTES.md

@@ -0,0 +1,23 @@
+# Design
+- core: only PSL
+- pass if modules are missing
+- minimize dependencies, code
+- test everything in the core framework
+
+# small stuff
+- rethink documentation (use mostly md files)
+- @parameter? (or was it @attribute?) - remove getter/setters
+- use __ for private
+
+## Improvements
+- API documentation
+- github pages
+
+## TODO
+- themes: use colors to improve theme readability
+- convert some stuff to simple attributes to reduce LOCs
+- use add_widget() instead of core.widget.Widget()
+- use widget index for bumblebee-ctl as alternative (??)
+
+# documentation
+Add info about error widget and events for error logging