Relaxed constraint on IMT and validate_hazard_metadata
parse imt also when the fragility model is continuous
improved error message
updated schema
Added comment on nrml_common schema
Merge pull request #75 from gem/relax_constraint_imt_type_validate_hazard_metadata

Relaxed constraint on IMT and validate_hazard_metadata
allow empty IML in continuous case
set imls to None in the continuous case
Merge pull request #76 from matley/fragility-continuous-fix

Continuous Fragility Model fix
write mean/stddev in scenario case
fixed test against None singleton
Merge pull request #77 from matley/scenario-export-fix

write mean/stddev in scenario case