Add function to convert sf line representation to 'odf' representation

This is a sub-task of #20, with a view to splitting the task into small and manageable sub-tasks. You up for giving it a bash @mtennekes?

Start by reading the parent issue #20 to understand the required sf line and odf representations. Locate the package's existing conversion functions or entry points, then confirm that the requested conversion is implemented and covered by the relevant tests.

Written by the indexing model from the issue text.