Contentful-management

* Adds support for cross-space references

* Preserve fields default values when updating content type [90](https://github.com/contentful/contentful-management.py/issues/90)

Fixed
* Bug in creating entry when no metadata is provided [97](https://github.com/contentful/contentful-management.py/issues/97)

* Changed CI/CD vendor from Travis to CircleCI
* Fixed typo in readme
* Added Support for Tags API
* Update CircleCI config to use latest Python version

Added
* Adds find user in space or organization scope [66](https://github.com/contentful/contentful-management.py/pull/66)

*Note*: Only a minor change because the removed feature was *Alpha*.

Added
* Add `OrganizationPeriodicUsage`, `Clientorganization_periodic_usages` and `Organizationperiodic_usages`.
* Add `SpacePeriodicUsage`, `Clientspace_periodic_usages` and `Organizationspace_periodic_usages`.

Removed
* Removed now deprecated Alpha Usage APIs, which have been superseeded by the new APIs added.