Issue 8

[hentai-chan]

This PR resolves issue #8:

• adds a check_manifest function to gen_data.py
• updates requirements.txt (a vulnerability was found in pillow, but I also removed click because all CLI-related code was rather verbose for all intents and purposes)
• I also suggest using --only-binary all whenever possible to disable sdist installations (all major packages ship with wheels but it's a good habbit to develop for anything else)
• redefines the commands in the python script to make creating assets easier:

$ # creates two new pkmn data sets (sprite + data)
$ python gen_data.py --verbose make --id 1 4
$ # create manifest.json
$ python gen_data.py manifest

• implements a function for resolving the assets path:

auto assets = find_upwards("assets");
std::cout << assets.string() << '\n';
std::cout << std::filesystem::exists(assets) << '\n'; // 1

This basically wraps up almost all preliminaries, up next are djson integration into the project and reading from the assets file in the Pokemon structure (issue #9)

[hentai-chan]

I just noticed that I didn't update the README file completely, the --name option in gen_data.py was deprecated, I'll correct this on Sunday. It's a trivial error so I'll make this change together with issue #9