Add option for embedded config and fallback resources

[Kuuuube]

Partial fix for #218

Allows static binaries to function properly in rust by falling back on default config and resources. Missing support for user defined embedded files but I think sudachi.rs should have at least basic support for static binaries.

Basic example code creating a tokenizer using embedded defaults (dictionary must still be added separately):

let embedded_dictionary = include_bytes!("./system_full.dic");
let sudachi_dic_data = SudachiDicData::new(Storage::Borrowed(embedded_dictionary));
let config = Config::new_embedded().unwrap();
let japanese_dictionary = JapaneseDictionary::from_cfg_storage_with_embedded_chardef(&config, sudachi_dic_data).unwrap();

let tokenizer = StatelessTokenizer::new(&japanese_dictionary);

[mh-northlander]

Ideally the embedded resource files should be used as a system default (replacing current default-resource-directory based configuration).
But as a first step we can have both.

I accept this PR with some miner changes.

[Kuuuube]

Thank you for the review! Everything should be resolved.

[mh-northlander]

@Kuuuube please apply cargo fmt.

[Kuuuube]

Done