fix for #158 by returning NaN when possible

prep for release

fix bug introduced in v0.2.8

thanks very much to Steve for reporting and providing test-case.

prep for release

bump version

update docker file

closes #97

fix long-standing bug (#27) that would cause sigsegv in some cases

compound-hets: write summary even if no variants

update link in tsv help to new hpo file

closes #91