Kinto-attachment

**Bug fixes**
- Update the call to the Record resource to use named attributes. (97)

- Add the gzip option to automatically gzip files on upload (85)
- Run functional test on latest kinto release as well as kinto master (86)

Update to `kinto.core` for compatibility with Kinto 3.0. This release is no longer compatible with Kinto < 3.0, please upgrade!

**Bug fixes**
- Fix MANIFEST.in rules in packaging

**New features**
- Add ability to disable filename randomization using a `?randomize=false` querystring (62)
- Add a `--keep-filenames` option in `upload.py` script to disable randomization (63)

**Bug fixes**
- Fix a setting name for S3 bucket in README (68)
- Do nothing in heartbeat if server is readonly (fixes 69)

**Internal changes**
- Big refactor of views (61)

**New features**
- Previous files can be kept if the setting `kinto.keep_old_files` is set
to `true`. This can be useful when clients try to download files from a
collection of records that is not up-to-date.
- Add heartbeat entry for attachments backend (41)

**Bug fixes**
- Now compatible with the default bucket (42)
- Now compatible with Python 3 (44)

**Internal changes**
- Upload/Download scripts now use `kinto.py` (38)