Added include_paths option to whitelist files & paths

[niekdomi]

This option was quite convenient when developing a cli for codebook and i think its a nice addition to the ignore_paths. E.g., if only .rs files should be linted, I think it's better to use the include_paths rather than ignoring everything with ignore_paths.

[blopker]

Thanks for this. Can you describe in more detail how include_paths and ignore_paths should interact with each other? Maybe the config should be invalid if both are included?

[niekdomi]

The idea is basically:

• include_paths: whitelist, only list files, filetypes, directories that should be linted
• ignore_paths: blacklist, files etc. that should not be linted.

Let's say you only want codespell to only lint rust files, instead of adding every other file etc. to the ignore_paths, the include_paths can be used.

They are complementary, though ignore_paths has higher precedence. So e.g.,

include_paths = [
    "**/*.yaml",
]
ignore_paths = [
    "**/*.yaml",
]

would lint nothing.

Should I add some test cases to "demonstrate" the expected behavior?