convert strategy to enum; cleanup renderer.rs imports; cleanup converter.rs functions

[Crypto-Spartan]

This should work properly, it is able to compile without issue. However, I had issues with opencv (I'm using repl.it) so I couldn't test the full functionality.

In converter.rs, you had redundant match statements as well as redundant functions (to_ascii & to_ascii_color). I removed the redundant parts and simplified the code. Additionally, I was able to remove the error paths from the match statement since matching on an enum in Rust is exhaustive.

Let me know if you have any questions about the changes I made, happy to explain if needed.