UTIL: Added a utils file with solve_discrete_lyapunov and put in init file.
Changed the code in quad sums to call the util folder solve_discrete_lyapunov code.
TESTS: Adding tests for solve_discrete_lyapunov
LYAP: Changed the imports to use the doubling alg.
LYAP: Created a file called matrix_eqn and put riccati and lyapunov solvers in it.  Changed other files to reflect this change.
TESTS: Added some basic tests.
Merge branch 'master' of github.com:jstac/quant-econ into lyap
LYAP: Changed the call in evans_sargent.py to use quantecon lyapunov solver.
LYAP: Fixed the tests and corrected calls.
Merge pull request #48 from jstac/lyap

Lyapunov