Miss the history of API version

[hongbin]

Nova has a history of each API version: https://github.com/openstack/nova/blob/master/nova/api/openstack/api_version_request.py#L41 . We should do something similar in Magnum.

Below is the list of commits which bump the API version:
1.1 Initial version
1.2 https://github.com/openstack/magnum/commit/bf30b9b4cb51fb4c09cfc1b1c099f3773a5ace33
1.3 https://github.com/openstack/magnum/commit/63b5c21c8dc998772cb5933babac0bcf8c9c62eb

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/359176

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/359176
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=06d5bb54bd646cdfa5d1af5170178485e18b900d
Submitter: Jenkins
Branch: master

commit 06d5bb54bd646cdfa5d1af5170178485e18b900d
Author: yatin <email address hidden>
Date: Tue Aug 23 16:38:52 2016 +0530

    Add history for API versions supported by magnum

    Added history for API versions supported by magnum
    till date. For all newly added api, versions.py and
    rest_api_version_history.rst should be updated.

    Also added docs that describe what to do when a new
    microversion is added.

    The docs changes are taken from nova.

    Change-Id: Ia8c7f1e8536ef7820958aa73afae7e5b85672d54
    Closes-Bug: #1615843

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/magnum 3.0.0 release.