Interactive mode

[hallucino]

Add an interactive mode when the binary is run without arguments:

• [x] add a new state for this new mode
• [x] list all px8/p8 files in the current directory
• [x] handle correctly multiples cartridges
• [x] add a new menu to display the current cartridges

[hallucino]

I added a basic menu to show px8/p8 files, and the logic to switch to another cartridge via the menu.

[hallucino]

I will work more correctly on a better menu for the next version.

You could get the menu in a game via: pause -> quit

or directly without any cartridge argument: ./target/release/px8 -s 4