* remove `.endian()` method in favor of data descriptor `.endian`
* allow bitarray initializer `bytes` or `bytearray` to set buffer directly
* allow calling `.extend()` with `bytes` object (although the only
valid bytes are 0x00 and 0x01)
* add `util.byteswap()`
* add `util.correspond_all()`
* fix `.reverse()` for imported buffer
* drop Python 3.5 support
* add tests
OBS-URL: https://build.opensuse.org/package/show/devel:languages:python/python-bitarray?expand=0&rev=62
