Enable use of dynamic number of residuals for autodiff.
Implemented with "Substitution failure is not an error" similar
to tiny_solver.h .
Move test from tiny_solver_test.cc to
tiny_solver_autodiff_function_test.cc .
Use cpplint.py from C++ Google Style Guide for formatting.
Change-Id: I2e1a159d17118552943c6ac7a833c5bbd0c927ec