JL: Added discrete_lyapunov.
JL: Matrix_eqn.jl.  Added the new doubling algorithm, rearranged files and added matrix_eqn to the module.
MERGE: Pulled master into this branch for easier PR acceptance.  Alphabetized QuantEcon.jl
JL: Changed references to dare to solve_discrete_riccati and updated module file.
JL: Removed old riccati reference from module file.
JL: Fixes to matrix_eqn.
JL: Made kalman.jl match kalman.py and made small changes to solve_riccati etc...
JL: Changed lq to be right order for solve_discrete_ricatti
MERGE: merged matrix_eqn branch into master