Smart-open

- Don't use s3 bucket_head to check for bucket existence (PR [315](https://github.com/RaRe-Technologies/smart_open/pull/315), [caboteria](https://github.com/caboteria))
- Dont list buckets in s3 tests (PR [318](https://github.com/RaRe-Technologies/smart_open/pull/318), [caboteria](https://github.com/caboteria))
- Use warnings.warn instead of logger.warning (PR [321](https://github.com/RaRe-Technologies/smart_open/pull/321), [mpenkov](https://github.com/mpenkov))
- Optimize reading from S3 (PR [322](https://github.com/RaRe-Technologies/smart_open/pull/322), [mpenkov](https://github.com/mpenkov))

- Improve S3 read performance by not copying buffer (PR [284](https://github.com/RaRe-Technologies/smart_open/pull/284), [aperiodic](https://github.com/aperiodic))
- accept bytearray and memoryview as input to write in s3 submodule (PR [293](https://github.com/RaRe-Technologies/smart_open/pull/293), [bmizhen-exos](https://github.com/bmizhen-exos))
- Fix two S3 bugs (PR [307](https://github.com/RaRe-Technologies/smart_open/pull/307), [mpenkov](https://github.com/mpenkov))
- Minor fixes: bz2file dependency, paramiko warning handling (PR [309](https://github.com/RaRe-Technologies/smart_open/pull/309), [mpenkov](https://github.com/mpenkov))
- improve unit tests (PR [310](https://github.com/RaRe-Technologies/smart_open/pull/310), [mpenkov](https://github.com/mpenkov))

- Removed dependency on lzma (PR [262](https://github.com/RaRe-Technologies/smart_open/pull/282), [tdhopper](https://github.com/tdhopper))
- backward compatibility fixes (PR [294](https://github.com/RaRe-Technologies/smart_open/pull/294), [mpenkov](https://github.com/mpenkov))
- Minor fixes (PR [291](https://github.com/RaRe-Technologies/smart_open/pull/291), [mpenkov](https://github.com/mpenkov))
- Fix 289: the smart_open package now correctly exposes a `__version__` attribute
- Fix 285: handle edge case with question marks in an S3 URL

This release rolls back support for transparently decompressing .xz files,
previously introduced in 1.8.1. This is a useful feature, but it requires a
tricky dependency. It's still possible to handle .xz files with relatively
little effort. Please see the
[README.rst](https://github.com/RaRe-Technologies/smart_open/blob/master/README.rst#supported-compression-formats)
file for details.

- Added support for .xz / lzma (PR [262](https://github.com/RaRe-Technologies/smart_open/pull/262), [vmarkovtsev](https://github.com/vmarkovtsev))
- Added streaming HTTP support (PR [236](https://github.com/RaRe-Technologies/smart_open/pull/236), [handsomezebra](https://github.com/handsomezebra))
- Fix handling of "+" mode, refactor tests (PR [263](https://github.com/RaRe-Technologies/smart_open/pull/263), [vmarkovtsev](https://github.com/vmarkovtsev))
- Added support for SSH/SCP/SFTP (PR [58](https://github.com/RaRe-Technologies/smart_open/pull/58), [val314159](https://github.com/val314159) & [mpenkov](https://github.com/mpenkov))
- Added new feature: compressor registry (PR [266](https://github.com/RaRe-Technologies/smart_open/pull/266), [mpenkov](https://github.com/mpenkov))
- Implemented new `smart_open.open` function (PR [268](https://github.com/RaRe-Technologies/smart_open/pull/268), [mpenkov](https://github.com/mpenkov))

smart_open.open

This new function replaces `smart_open.smart_open`, which is now deprecated.
Main differences:

- ignore_extension → ignore_ext
- new `transport_params` dict parameter to contain keyword parameters for the transport layer (S3, HTTPS, HDFS, etc).

Main advantages of the new function:

- Simpler interface for the user, less parameters
- Greater API flexibility: adding additional keyword arguments will no longer require updating the top-level interface
- Better documentation for keyword parameters (previously, they were documented via examples only)

The old `smart_open.smart_open` function is deprecated, but continues to work as previously.

- Add `python3.7` support (PR [240](https://github.com/RaRe-Technologies/smart_open/pull/240), [menshikh-iv](https://github.com/menshikh-iv))
- Add `http/https` schema correctly (PR [242](https://github.com/RaRe-Technologies/smart_open/pull/242), [gliv](https://github.com/gliv))
- Fix url parsing for `S3` (PR [235](https://github.com/RaRe-Technologies/smart_open/pull/235), [rileypeterson](https://github.com/rileypeterson))
- Clean up `_parse_uri_s3x`, resolve edge cases (PR [237](https://github.com/RaRe-Technologies/smart_open/pull/237), [mpenkov](https://github.com/mpenkov))
- Handle leading slash in local path edge case (PR [238](https://github.com/RaRe-Technologies/smart_open/pull/238), [mpenkov](https://github.com/mpenkov))
- Roll back README changes (PR [239](https://github.com/RaRe-Technologies/smart_open/pull/239), [mpenkov](https://github.com/mpenkov))
- Add example how to work with Digital Ocean spaces and boto profile (PR [248](https://github.com/RaRe-Technologies/smart_open/pull/248), [navado](https://github.com/navado) & [mpenkov](https://github.com/mpenkov))
- Fix boto fail to load gce plugin (PR [255](https://github.com/RaRe-Technologies/smart_open/pull/255), [menshikh-iv](https://github.com/menshikh-iv))
- Drop deprecated `sudo` from travis config (PR [256](https://github.com/RaRe-Technologies/smart_open/pull/256), [cclauss](https://github.com/cclauss))
- Raise `ValueError` if s3 key does not exist (PR [245](https://github.com/RaRe-Technologies/smart_open/pull/245), [adrpar](https://github.com/adrpar))
- Ensure `_list_bucket` uses continuation token for subsequent pages (PR [246](https://github.com/RaRe-Technologies/smart_open/pull/246), [tcsavage](https://github.com/tcsavage))

- Unpin boto/botocore for regular installation. Fix 227 (PR [232](https://github.com/RaRe-Technologies/smart_open/pull/232), [menshikh-iv](https://github.com/menshikh-iv))