Libarchive-c

Changes to the library:

- optimized the `ArchiveEntry` class (94)
- added support for the `zstd` format (90)
- fixed the top-level `__all__` list (7b97d8b903ad1a5032938e9c4a7100c4a27b3cb9)
- updated the code to support Python 3.8 (88)
- improved the `add_file_from_memory` method (85 and 86)
- lowered the level of log messages from warning to info (83)

Tests:

- dropped testing with Python 3.4, added 3.7 and 3.8 (88)
- fixed unicode handling in entry tests (84)

Changes to the library:

- add support for setting `atime`, `ctime`, `mtime` and `birthtime` (50 and 63)
- tell libarchive when writing an archive is aborted due to an exception (53)
- add support for getting `uid` and `gid` (57)
- add support for high resolution timestamps (58)
- add two new archive readers: `stream_reader` and `custom_reader` (60)
- add missing archive extraction flags (61)
- add the `lz4` and `warc` formats (62)
- add support for write options and uid/gid lookup (72)

Tests:

- drop python 3.3 and add 3.6
- add segfault detection (59)
- test against libarchive 3.3.2 instead of 3.1.2 (70)

Changes to the library:
- only read regular files (47)
- add support for `atime` and `ctime` (49)

Changes to the library:
- small tweak for better compatibility with python 2.6 (37)
- new `add_file_from_memory` method (38)
- fix int type to allow working with large files (41)

Tests:
- we now use `tox` (40)

Changes to the library:
- don't hardcode errno constants (33)

Packaging:
- set umask to `022` in `setup.py` (36859c99e270a95da479a9732f4385fdcd98d8b8)

Tests:
- fix a test to be compatible with libarchive 3.2 (35)

This is a fix release that doesn't change the library code. Details:
- fixed file permissions in PyPI archives (30)
- fixed Travis CI builds (32)