3.0

Changes to the library:

• BREAKING: dropped support for Python 2.7 (#108)
• implemented reading and writing encrypted archives (#109)
• created a new context manager: seekable_stream_reader (#107)
• added support for 64-bit time_t on 32-bit systems (#101)
• load extra formats and filters when they're requested (#95)

Tests:

• dropped testing with Python 2.7 and 3.5, added 3.9 (#108)