Framework for writing a legend file
Field descriptions for interpreters
make tests pass
Bugfix: Legend file name needs to be unique

When there are multiple reports in a plan file they will be written to the
same directory. The legend files are unique to a report. With the old naming
scheme the legend file names would clash if there were more than one. Now
they're being created uniquely by using each report's name.
Encode the list of filters to be excluded from the legend file in a more generic way
Merge pull request #37 from susannasiebert/cle_legend_file

Create a legend file for CLE reports