release-3.0.0

• This is a major release due to packaging changes, although there are no backward incompatible interface changes.
• The cloudbridge package no longer installs any providers by default, and you must use pip install cloudbridge[full] instead of pip install cloudbridge to obtain previous behaviour. This is to allow greater control over what providers are installed. To install only specific providers, use pip install cloudbridge[aws,gcp] etc. #292 (thanks to @RyanSiu1995)
• Allow users to create signed urls with write permissions #294 (thanks to @FabioRosado)

Full Changelog: v2.2.0...v3.0.0