Add support for excluding files about phar-composer HOT 1 OPEN

For now, this requirement can simply be avoided by using a simple build script as suggested in #91 to delete all unwanted files from a temporary build directory.

In the future, we may implement explicit support for excluding certain files. Some inspiration can be taken from Symfony's Finder component in https://github.com/symfony/finder/blob/bd866ffc62322350897dac99d1cf96b1b5879700/Gitignore.php and https://github.com/symfony/finder/blob/bd866ffc62322350897dac99d1cf96b1b5879700/Finder.php#L699. This feature is built into 4.3+, but we can't currently depend on this version without breaking BC. Being MIT-licensed, we can probably reuse some of this use without adding a dependency.

from phar-composer.