Clean up utils.
Instrument MINRES with check_symmetric.
Add check_symmetric in utils.
First step towards proper MINRES integration.

MINRES is not yet properly a subclass of the generic Krylov solver
class, but now has a few of its basic attributes.
Common code for demos.
Demo for MINRES.
Samply symmetric indefinite matrix.
Fix MINRES exit codes.
Add demo for CG.
Add spd test matrix.
Add option to check symmetry in CG.
Upgrade some logging to error level.
Pass logger option to solver in demo.
Add logger in CG demo.
Update README.
fixed full form of tfqmr
Merge pull request #2 from nunoxic/master

QMR was incorrectly expanded to Minim*um* Residual (instead of the correct, Minim*al* Residual)
Update pykrylov/tfqmr/tfqmr.py
Merge pull request #4 from nunoxic/patch-2

Update pykrylov/tfqmr/tfqmr.py
Minor cleanup in linop.