Classification of nonlinear sysode for 1st order 3 eq

This commit has the method to classify nonlinear system of 3 ODEs of first order. It contain six type of equation which considered here.
method for 3 type of 3 nonlinear sysode of 1st order

This contains definition of sysode_nonlinear_3eq_order1 and definition for solving three types of 3 nonlinear system of ODEs of first order.
nonlinear sysode 3eq order1 type4
Added type5 and few test cases
Updated tests
Updated syntax of dict values
corrected list of solve output
docs of nonlinear sysode of 3 eq 1st order
Merge pull request #7703 from KDMOE/sysode_nonlinear_order1_3eq

Classification of nonlinear sysode for 1st order 3 eq