Yadisk

* Added the missing parameter `sort` for `get_meta()`
* Added `file` and `antivirus_status` attributes for `ResourceObject`,
`PublicResourceObject` and `TrashResourceObject`
* Added `headers` parameter
* Fixed a typo in `download()` and `download_public()` (`issue 2`_)
* Removed `*args` parameter everywhere

* Fixed `timeout=None` behavior. `None` is supposed to mean 'no timeout' but
in the older versions it was synonymous with the default timeout.

* Changed the license to LGPLv3 (see `COPYING` and `COPYING.lesser`)
* Other package info updates

* Fixed a couple of typos: `PublicResourceListObject.items` and
`TrashResourceListObject.items` had wrong types
* Substitute field aliases in `fields` parameter when performing
API requests (e.g. `embedded` -> `_embedded`)

* Fixed a file rewinding bug when uploading/downloading files after a retry

* Now caching `requests` sessions so that open connections
can be reused (which can significantly speed things up sometimes)
* Disable `keep-alive` when uploading/downloading files by default