Edit convergence script for cylinder at Re=40.

* Remove the shell script to run the cases.
* Add .gitignore file.
* Remove .hgignore file.
Check convergence of cavity flow.

* Add cases for lid driven cavity at Re=100.
* Four uniform meshes of side 32, 96, 288 and 864.
* Write scripts to run the cases and calculate order of convergence.
* Minor edit to .gitignore file.