API does not support usernames with periods in them

[UweTrottmann]

The API (e.g. /users/:user/friends) might return a username that contains a period ., e.g. Prof.JensDrehbares.

However, calling any /user method with this username will result in an error or unexpected response, as the API expects periods to be encoded as dashes -, e.g. Prof-JensDrehbares.

Asked Justin on Google+ about documentation of any other possible character replacments.