feat: generate issues from source and refactor to make it as a library

[0xtekgrinder]

This PR adds a few things:

• process source instead of filename to generate issues
• refactor main.go to be used partially as a library by creating a lint.go file and making logs optional
• fix a little typo GenetateFormattedIssue instead of GenerateFormattedIssue

Some of this code is far from perfect for example:

var node *ast.File
	var err error
	if content == nil {
		node, err = parser.ParseFile(fset, filename, nil, parser.ParseComments)
	} else {
		node, err = parser.ParseFile(fset, filename, content, parser.ParseComments)
	}
	if err != nil {
		return nil, nil, err
	}

Which was created to "fix" the issue that nil wasn't taken into account when using parser.Parsefile with an indirect function argument

[notJoon]

maybe we should change the directory name from lints to something else someday to avoid confusion with the newly added lint directory.

[notJoon]

This was something need to be done at someday, and it seems resolved now. I have a feeling that ParseFile will need some modification later, but not sure about it right now.

Thanks 👍