Cythonize generated router code

[kgriffs]

Let's consider using cython.inline() to compile the generated router code. If we do this, we will need to be very transparent about what it is doing, and also fall back if the compilation fails due to a missing compiler, etc. Also we would need to solve #1550 first.

By default, cython.inline() behaves as follows (according to @vytas7's testing):

• Saves the snippet to a temporary file (e.g., ~/.cython/inline/_cython_inline_7723cfda1cea8e31cc3829cad4d730f3.pyx)
• Cythonizes the temporary *.pyx file
• Imports and returns the compiled module

[kgriffs]

Note that even once #1550 is solved, we will still need to document that compiling it could take a few moments, slowing down the first request (if that is how we implement #1550).