Allow subfolders in a cheats dir

This change allows you to have subfolders within your cheats directory. Here's some use cases:

- Sarah keeps a public github repo of cheats, but respects her friends Tom and Rachael, so she submodules their public cheat repos into hers. They appear in hear ~/.cheat folder as subfolders, and cheat recognises them automatically.
- James keeps a public repo of cheats, but also shares some for company specific code in a private company repo. He encourages all the company devs to check out the company cheat repo into their ~/.cheat folder, and so to help each other with common commands.

The core idea: having subfolders makes cheat much more sharing-friendly.