Properly handle cases when number extremum is 0

The condition does not hold when `schema.minimum` or `schema.maximum` equals 0, even if the property actually defined.
Merge branch 'keynslug-patch-1'
Standardize all notify/change/watch calls. Fixes #247 Fixes #248

Probably fixes a lot more bugs too
Fix array/minItems bug. Fixes #246
Add option to remove empty object properties from returned JSON. Fixes #220
Version bump to 0.7.10