Consider adding an option to normalize whitespace in descriptions

[gtback]

When description fields contain multi-line/formatted text (including HTML), whitespace present in the XML may not lead to "pretty" descriptions in JSON. This would essentially require doing description = ' '.join(description.split())

This should NOT be the default behavior.

Note that should not apply to whitespace between fields that get added to the STIX 2.0 description because there is no equivalent field in STIX 2.0 for some STIX 1.x field; those should continue to be separated by newlines.