Proposal: Add optional Basic Theta* support #63

Hi,

I am a student working on an academic open-source project and am considering contributing support for Basic Theta* to this library.

Since python-astar currently provides a generic graph-oriented A* API, my proposed contribution would add a compatible Theta* variant with explicit hooks for:

• checking line of sight between a node's parent and a candidate node;
• computing distance between visible, non-adjacent nodes;
• preserving the existing A* API and behavior;
• tests and documentation, including a 2D grid example.

Before starting, I would like to ask whether this feature fits the scope of the library and whether you would be open to reviewing such a pull request. I would also appreciate any preferences regarding the API design.

Paper: Theta*: Any-Angle Path Planning on Grids

Thank you!