Save flow variables and grid using binary format.
Read binary data from saved files.

* Edit readData.py to read grid and velocities.
* Edit plot extents in plotVorticity.py.
Merge branch 'new-io'
Increase permitted folder name length to 256.
Add convergence test for NavierStokesSolver.

* Lid-driven cavity at Re=100 starting with 20x20 and 32x32 grids.
* Edit .gitignore.