Add the mechanism for collecting and reading the following events:

• "John Doe registered" (user created)
• "John Doe updated the account" (user updated)
• "John Doe deleted his account" (user deleted)
• "John Doe added a new post" (post created)

These are high-level descriptions that could be displayed by the client application. From the internal system, it needs to be possible to see more details about a given event (for example, which fields of the user were updated or what e-mail address has been used to add a new account).

All events need to be persistent. Also, they have to be stored in the separate data store from the main database.

Summary:

• Use a separate data store for events (it can be any engine - there is no need to worry about the performance)
• Events need to be persistent
• Collect events listed at the beginning
• Expose API for reading events

Configure credo and dialyxir and add a mix check task.

Currently, the access is public which means that credentials are not needed to, for example, delete an existing user with all associated posts.

This ticket covers the following subtasks:

• add sessions controller that allows login and implements "whoami" functionality
• allow public access only to "get posts" endpoint
• allow deleting user only by himself
• allow updating user only by himself
• deny creating posts that are associated with other users