Convert from using --path to using --use-script-input-files

[kylefleming]

This converts from making a separate call to swiftlint for each file using --path to passing all files in at once using --use-script-input-files.

This is how danger/swift and fastlane/swiftlint do it and I believe it is the recommended way of linting specific files.

The biggest motivation for me for doing this is to allow nested configurations. Since passing a single file to swiftlint changes the "root folder" from the location of the main config file to the location of the swift file, swiftlint isn't able to traverse up the tree from the swift file up to the main config file looking for nested .swiftlint.yml files. By using --use-script-input-files instead of --path, swiftlint is able to find nested config files properly.

I suspect this change will have other benefits as well and could possibly have better performance.

Feel free to make or suggest any changes.

Closes #111 (and possibly related to #87)

[ashfurrow]

Wow, this is impressive work 🙏 The motivation for the changes you outlined in the PR description makes perfect sense, I agree this is a good idea. The implementation and tests look fantastic – thanks for taking the time to cleanup Shellwords and the unit test stubs. The only thing missing is a changelog entry, but I'll do that myself.

Thanks again for contributing to the tool – I'll get this released to RubyGems this afternoon.

[ashfurrow]

Okay, that's released as 0.23.0 👍