Improve docstrings of builtin routing classes.
Improve docstrings of builtin routing classes.

harrissoerja/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi,TouK/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi,TouK/vumi,vishwaprakashmishra/xmatrix,TouK/vumi