Blobxfer

Added
- Allow storage account or sas key credentials to be passed as
environment variables

Added
- Azure Files support, please refer to the General Notes section for
limitations

Changed
- `--blobep` option has been renamed to `--endpoint`

Changed
- Update all dependencies to latest versions
- Add flag for block/page level md5 computation which is now disabled by
default

Fixed
- Update against breaking changes from azure-storage 0.32.0

Removed
- Remove RC designation from encryption/decryption functionality

Security
- Update cryptography requirement to 1.4

Added
- Added ``--disable-urllib-warnings`` option to suppress urllib3 warnings
(use with care)

Changed
- Update script for compatibility with azure-storage 0.30.0 which
is now a required dependency
- Promote encryption to RC status
- `--blobep` now refers to endpoint suffix rather than blob endpoint
(e.g., core.windows.net rather than blob.core.windows.net)

Security
- Update cryptography requirement to 1.3

Changed
- Pin azure dependencies due to breaking changes

Fixed
- Minor bug fixes

Security
- Update cryptography requirement to 1.2.2