py-libarchive-c: updated to 2.9

2.9:
Changes to the library:
optimized the ArchiveEntry class
added support for the zstd format
fixed the top-level __all__ list (7b97d8b)
updated the code to support Python 3.8
improved the add_file_from_memory method
lowered the level of log messages from warning to info

Tests:
dropped testing with Python 3.4, added 3.7 and 3.8
fixed unicode handling in entry tests

(adam)