Replace assert(0) with a self-documenting TODO string
Merge pull request #660 from Rosuav/assert0

Replace assert(0) with a self-documenting TODO string
py: Make import recognize and load native modules (.pyd or .so files)

Simply check if a .pyd or .so file exists on the Python search path
(if a .py file if not found) and call a function to get a module from it
msvc: Implement LoadDynLib
msvc: Make part of uPy dynamically loadable via import lib

Exports some core functions using exports.def, export constants/data using the
typical dllexport (exporting data using .def file yields multiple copies of data).
Create an import lib next to micropython.exe whcih can be used by modules.
msvc: Add property sheet for building native modules, update README