Sysode docs

It contains the docs of all implemented method to solve for system of ordinary differential equations which include 
 linear system of 2 equations of 1st order,
 linear system of 2 equations of 2nd order,
 linear system of 3 equations of 1st order,
 linear system of n equations of 1st order,
 non-linear system of 2 equations of 1st order
@tjl @flacjacket TEST_SPHINX is failing due to indentation error. Is it because of the indentation here? but I build the doc locally, and it was build without any error.