Added a fluid simulation example

Description

Added a Lattice Boltzmann Computational Fluid Simulation Example to the ArrayFire example list. It was added to the pde folder and it contains 9 images that were added to the assets/examples/images repo folder. It contains three distinct initial conditions for the user to try.

• Is this a new feature or a bug fix?: Neither
• Potential impact on specific hardware, software or backends: None
• New functions and their functionality: None
• Can this PR be backported to older versions?: Yes
• Future changes not implemented in this PR: None

Changes to Users

• New example project in the arrayfire example list
• No action required by the user

Checklist

• Rebased on latest master
• Code compiles
• Tests pass
• Functions added to unified API
• Functions documented