add option to configure a complex api url pattern
feature #18 add option to configure a complex api url pattern (xabbuh)

This PR was merged into the 1.0-dev branch.

Discussion
----------

add option to configure a complex api url pattern

see #17 for the background of this pull request

Commits
-------

7818747 add option to configure a complex api url pattern
method `utils.escape()` does not exist

The `utils` module from the docutils package doesn't provide an
`escape()`  method.
ensure that `base_url` is a string

The default value of the `api_url` config option is an empty dict.
Therefore, if the user didn't explicitly configure a value for it,
print the error message will fail since a dict cannot be appended
a string.