Linear coefficients- first implementation
Nested functions are also classified
Using find to classify nested functions
refactor linear_coefficients
proceed if c1 or c2 is not zero
Added helper functions, new tests
Made changed
minor edits to ode.py
Merge pull request #5 from smichr/lincoff

minor edits to ode.py
Merge pull request #1940 from Manoj-Kumar-S/lincoff

Differential equations with linear coefficients