'Return a dictionary representation of sections and subsections.
Example:
\'Introduction\': [\'Course Overview\'],
\'Week 1\': [\'Lesson 1\', \'Lesson 2\', \'Homework\']
\'Final Exam\': [\'Final Exam\']
You can use these titles in `go_to_section` to navigate to the section.'

@property
def sections(self):

    outline_dict = OrderedDict()
    section_titles = self._section_titles()
    for (sec_index, sec_title) in enumerate(section_titles):
        if (len(section_titles) < 1):
            raise ValueError("Could    not    find    subsections    for    '{0}'".format(sec_title))
        else:
            outline_dict[sec_title] = self._subsection_titles((sec_index + 1))
    return outline_dict
