Bugfix: don't allocate bigM/normal until needed
Bugfix for nil ptr panic if switching to normal during Cardinality()
	JSON marshalling for save/restore of Hll in progress. Fixes #5

Uses snappy to reduce the size of the JSON.
More concise base64ing, per schmichael's PR feedback
Merge pull request #6 from lytics/jsonmarshal

JSON marshalling for save/restore of Hll in progress