Add JSON field

Merge pull request #3 from nyaruka/json

add json nullable type

Change StringMap to Map

Allows for arbitrary values in maps.

Add StringMap type

Add new types that allows for text representation of a map[string]string in the DB and JSON while writing nulls for both as needed.

Simplify boilerplate

v1.0.3

Merge branch 'master' of github.com:nyaruka/null

Initial Release

v1.0.2

Merge branch 'master' of github.com:nyaruka/null

Initial release

v1.0.0

Update README.md