Project initialization

[frohrlich]

Initial implementation of scim2-flask.

SCIM2 serves the resource, search, bulk and discovery endpoints of RFC 7644
over a ScimStorage the application implements, and a ScimProvider
describing the resource types and the supported features.

• validation and serialization with scim2-models, in the context of each
  operation and under the policy of the provider
• PUT and PATCH applied by the extension, persisted with a single storage
  update
• searches per resource type and at the server root
• bulk operations, with failOnErrors, maxOperations and maxPayloadSize
• conditional requests with ETags
• SCIM error payloads for every failure
• an in-memory example server, checked with scim2-tester
• documentation: tutorial, how-to guides, explanation and reference, with
  executed examples