Avoid the bug when no masses are provided (header)

Signed-off-by: Cristian Maureira-Fredes <cmaurei@aei.mpg.de>
Ignoring snapshots

Signed-off-by: Cristian Maureira-Fredes <cmaurei@aei.mpg.de>
Adding examples

Signed-off-by: Cristian Maureira-Fredes <cmaurei@aei.mpg.de>
Updating module with docstrings

Signed-off-by: Cristian Maureira-Fredes <cmaurei@aei.mpg.de>
Adding source file

Signed-off-by: Cristian Maureira-Fredes <cmaurei@aei.mpg.de>